Major interaction on record — check this product against your medications before combining. Based on 5 of 6 ingredients. Check your meds →
Dietary supplement

GF-G Ingredients & Drug Interactions

by Pure Herbs

GF-G label
See full label image
Liquid Category: Botanical
Most serious interaction: Major
Clinical methodology reviewed by · Updated Sep 9, 2026 · Label data from the NIH DSLD
What is this page for?

First and foremost: checking GF-G against your medications. The heart of this page is the interaction checker and the full interaction report — how this product’s ingredients may interact with prescription and over-the-counter medicines you may be taking.

Around that, we add a pharmacist’s high-level view of the product as a whole — what’s inside, the evidence for its stated use, how transparent the label is, and what safety data exists — so you can see the full picture in one place. It’s educational information from our licensed clinical databases and the clinical staff at HelloPharmacist — not medical advice — and we don’t sell or endorse products. Our editorial policy

The interaction bottom line Most serious interaction: Major

GF-G is a dietary supplement by Pure Herbs with 6 active ingredients. Its ingredients are commonly taken for thyroid support, iodine source, weight management.Based on those ingredients, 2,113 medications have a known interaction with it, the most serious rated major. The ingredients most likely to interact are Plantain Leaf Extract, Kelp Whole Algae Extract, Fennel Seed Extract. Use the checker below to test your specific medication, or read the full HelloPharmacist Interaction Report.

Jump to a section

Check Your Meds Against GF-G by Pure Herbs

Ask about any prescription or over-the-counter medication and we check it for interactions with GF-G by Pure Herbs — and tell you which ingredient is responsible.

Pharmacist-reviewed data Checks every ingredient Answer in seconds
Prefer a human? Send your question to our licensed pharmacists — free, answered by email within 24 hours.

HelloPharmacist Scorecard of GF-G by Pure Herbs

Our pharmacy team’s full take, with four database checks built into the cards below — a summary of what is known, not a grade of the product itself.

From our pharmacy team — supplement deep dive

Generated from HelloPharmacist’s pharmacist-curated databases and editorial rules · Last generated Jul 30, 2026

What’s inside

Low disclosure
Ingredient Transparency · database check
Low

Most active ingredients don't disclose an individual amount — you can't tell how much of each you're getting.

Why this rating?
  • The label discloses an exact amount for 0 of its 6 active ingredients.
  • “Proprietary Blend” is a proprietary blend — the label gives one combined amount (1,935 mg) without saying how much of each component you get.

Pure Herbs GF-G is a liquid supplement with 6 ingredients. The active components are kelp whole algae extract, bladderwrack algae extract (both sea vegetables rich in iodine), fennel seed extract, burdock root extract, plantain leaf extract, and hawthorn flower, fruit, and leaf extract.

Each brings its own traditional or studied role—the algae for minerals and iodine, fennel for digestive and menstrual support, plantain for constipation and heart health, burdock for general wellness, and hawthorn for cardiovascular function. The product contains no other inactive ingredients listed.

Does it work?

Not established
Evidence for Intended Use · database check
By FDA rules, dietary supplements can’t claim to treat, cure, or prevent disease — so labels speak in careful marketing language. We discern each product’s intended use from its name, label claims, and label statements, then grade the clinical evidence for that use. How these ratings are computed
Not established

The graded evidence we hold for these ingredients covers different conditions than the ones this product is marketed for, so there's no established rating for its stated use.

Why this rating?
  • The label markets this product for: Helps to nourish and support thyroid function.
  • We looked for evidence on: Hypothyroidism, Iodine deficiency, Thyroid health, Goiter.
  • The closest evidence on file: Fucus Vesiculosus is rated "Insufficient Reliable Evidence To Rate" for Hypothyroidism (Natural Medicines).
  • Also on file: Fucus Vesiculosus is rated "Insufficient Reliable Evidence To Rate" for Iodine deficiency.

The evidence for what this product can do is sparse. Hawthorn shows insufficient reliable evidence for angina, anxiety, arrhythmia, atherosclerosis, cardiovascular disease, or cognitive function in our data.

Kelp and bladderwrack similarly lack solid evidence for aging skin, cardiovascular disease, constipation, diarrhea, or dyspepsia. Fennel is possibly effective for menstrual cramps (dysmenorrhea) but has insufficient evidence for bronchitis, anxiety, or other conditions listed.

Plantain leaf extract is effective for constipation and likely effective for heart disease prevention, but the rest of the product's ingredients don't have established effectiveness ratings in our data.

The evidence, ingredient by ingredient Fucus Vesiculosus Fennel Burdock Black Psyllium Hawthorn

How safe is it?

Well-documented data
Safety Information · database check
Well characterized

Adverse-effect, pregnancy, and general safety data are on file for most of these ingredients.

Why this rating?
  • We hold adverse-effect (side-effect) data for 5 of the 5 matched ingredients.
  • Pregnancy & breastfeeding safety ratings cover 5 of 5.
  • General safety write-ups exist for 5 of 5.
  • Remember: this measures how much safety information exists. Thin data is not the same as being safe.

When taken orally, this product carries real safety concerns tied mainly to its algae content. Kelp and bladderwrack have high and variable iodine levels that can trigger goiter (swollen thyroid), overactive thyroid (hyperthyroidism), underactive thyroid (hypothyroidism), and rarely thyroid cancer.

There's a documented case of hyperthyroidism in a patient taking these algae with lithium. Fennel and hawthorn are generally well tolerated in normal use, but fennel can cause stomach upset, sun sensitivity, and allergic reactions in some people—rarely, seizures.

Burdock appears well tolerated as a food but has limited human safety data; allergic reactions including contact dermatitis have been reported. Plantain leaf extract is generally well tolerated with adequate fluids.

During pregnancy, the algae products are considered possibly unsafe due to excess iodine and potential heavy metal content; iodine also passes into breast milk and can affect a baby's thyroid, so these are best avoided while nursing. Fennel is also possibly unsafe in pregnancy and lactation due to hormone-like effects and limited safety data.

Burdock and hawthorn lack enough safety information for pregnancy or breastfeeding, so they should be avoided during these times.

Side effects, ingredient by ingredient Fucus Vesiculosus Fennel Burdock Black Psyllium Hawthorn

Meds to double-check

Major interaction found
Known Interaction Concern · database check
Major identified

At least one ingredient has a documented Major-severity interaction. Check your medications for a personalized result.

Why this rating?
  • 5 of the 5 matched ingredients can interact with medications — Black Psyllium, Burdock, Fennel, Hawthorn, Fucus Vesiculosus.
  • The most serious interaction on file is rated Major.
  • Some involve high-stakes drug classes: anticoagulant / antiplatelet drugs; heart-rhythm medications; lithium.
  • For scale: 2,114 individual medications appear in the full list. A big number alone doesn't make a product dangerous — what matters is whether YOUR medication is on it, so run yours through the interaction checker on this page.

Before taking this product, double-check with your own doctor or pharmacist if you use any of the following: nitrates or phosphodiesterase-5 inhibitors (sildenafil/Viagra, tadalafil/Cialis) for blood vessel or erectile function—hawthorn could dangerously drop your blood pressure; lithium for mood disorders; thyroid medications or antithyroid drugs; beta-blockers or calcium channel blockers for blood pressure or heart rate; blood thinners or antiplatelet drugs (warfarin, aspirin, clopidogrel); birth control pills or estrogen therapy; metformin for diabetes; carbamazepine or olanzapine for seizures or psychiatric conditions; ciprofloxacin or other antibiotics; or digoxin for heart failure. No interactions are documented for burdock in our data.

Check your own medication Run your meds through the checker above

The bottom line

Scorecard at a glanceFormula with limited ingredient disclosure with no established evidence rating for its marketed use. Major medication interactions have been identified, and safety information is well characterized.

This product is built on sea vegetables and herbal extracts with a long history of use, but it's not a simple grab-and-go supplement—particularly if you take medications for thyroid disease, heart problems, or blood clotting. The algae content alone means you'll want to check in with your own doctor or pharmacist before starting, especially if you're on lithium, thyroid meds, or blood thinners.

If you're pregnant, planning to become pregnant, or breastfeeding, skip this product and talk to your healthcare provider about alternatives.

Educational only — not medical advice; always confirm with your pharmacist. Our editorial policy · How we use AI

Assessment coverage: 6 of 6 active ingredients matched to our full ingredient reviews (monographs). Based on the product label dated Nov 22, 2022.

This Scorecard evaluates available label information, ingredient evidence, and known medication-safety considerations. It does not independently verify product identity, purity, potency, contamination, or manufacturing quality. How these ratings are computed

At a glance

General information

Key facts about GF-G, straight from the product label.

Brand Pure Herbs
Net contents 1 Fluid Ounce(s); 30 mL
Market status On market
Date entered into DSLD Nov 22, 2022
DSLD ID 280011
Product type Botanical
Supplement form Liquid
Dietary claims / uses All Other, Structure/Function
Intended target group(s) Adult (18 - 50 Years), Women (not pregnant or lactating)
From the label
Everything in this section is reproduced from the manufacturer’s own product label — it’s the label speaking, not HelloPharmacist. We show it so you can see exactly what the maker states; we don’t verify or endorse those statements.

Supplement Facts

The label details for GF-G by Pure Herbs, sourced from the NIH Dietary Supplement Label Database.

Supplement Facts

Daily Value (DV) Target Group(s):
Adults and children 4 or more years of age
Minimum serving Sizes:
2 mL
Maximum serving Sizes:
2 mL
Servings per container
15
IngredientAmount% DV
Proprietary Blend1935 mg--
Kelp Whole Algae Extract0 NP--
Bladderwrack Algae Extract0 NP--
Fennel Seed Extract0 NP--
Burdock Root Extract0 NP--
Plantain Leaf Extract0 NP--
Hawthorn Flower, Fruit, Leaf Extract0 NP--

Other ingredients: None

Tap any ingredient to jump to its full detail below.

Label statements
These statements are the manufacturer’s wording, reproduced from the product label — the label is saying it, not HelloPharmacist. We don’t verify or endorse them.
Suggested/Recommended/Usage/Directions

Directions: For adults, mix 2 mL (abt. 1/2 tsp) of extract in 2 fl. oz (60 mL) water one time daily preferably with a meal.

Shake well before use

Formulation

Helps to nourish and support thyroid function.

FDA Disclaimer Statement

This statement has not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease.

Precautions

Warning: Not intended for use by pregnant or nursing women. If you have a medical condition or are taking medication, consult your doctor prior to use.

Discontinue use and consult with your doctor if any adverse reactions occur.

Keep out of reach of children

Brand IP Statement(s)

Pure Herbs, Ltd. Natural Herbal Extracts

FDA Statement of Identity

Dietary Supplement

General Statements

"No expense has been spared to provide the finest nature has to offer."

Is this label outdated? Report a formula or label change and our pharmacy team will review it.

See for yourself

GF-G by Pure Herbs label

The label scan from the NIH Dietary Supplement Label Database. Tap to enlarge.

GF-G label

Label images are published by the NIH Dietary Supplement Label Database for the version of this product on file. Always read your actual product label.

View the full label (PDF)
What’s inside

The Ingredients in GF-G by Pure Herbs

These are the 6 active ingredients this product is made of. Select any to open its full monograph.

Serving size2 mL Dosage formLiquid Servings per container15 Amounts shown are per serving.

Most supplement products combine several ingredients, and a medication can interact with the product through any one of them. Each ingredient below shows whether it has known drug interactions.

Other (inactive) ingredients: None. These complete the product’s ingredient list but are not active constituents.

Interaction report

GF-G by Pure Herbs Drug Interactions

Want to check YOUR meds against GF-G?

Ask about interactions with your drugs in plain English — “Can I take it with lisinopril?” — and we find you the answer in seconds, ingredient by ingredient.

 Go to the checker
2,113Drugs
14 Major 804 Moderate 1,295 Minor

Ingredients driving the most interactions

Plantain Leaf Extract 2,025
Kelp Whole Algae Extract 891
Fennel Seed Extract 740
Hawthorn Flower, Fruit, Leaf Extract 191
Burdock Root Extract 122

Individual Drug Interactions

The ingredients in GF-G interact with 2,113 drugs. Click any drug to see the details.

5 of the 6 ingredients in GF-G interact with drugs. Each result below shows which ingredient is responsible. Plantain Leaf Extract Kelp Whole Algae Extract Fennel Seed Extract Hawthorn Flower, Fruit, Leaf Extract Burdock Root Extract

Each ingredient & the kinds of drugs it affects

For each ingredient in GF-G with known interactions, here are the types of medications they can affect. Open any type for the detail — or search your exact drug in the checker above.

Plantain Leaf Extract7 drug types · 2,025 drugs

Carbamazepine (Tegretol)

Theoretically, black psyllium might reduce the effects of carbamazepine and increase the risk for convulsions.
Theoretically, black psyllium might reduce carbamazepine absorption. A preliminary study using blond psyllium reported decreased carbamazepine bioavailability due to binding of the drug to psyllium, as well as reduction of available fluid in the gut for dissolution of the drug. This interaction may also occur with black psyllium.

Likelihood Probable Evidence D
Lithium

Theoretically, taking black psyllium at the same time as lithium might reduce lithium absorption.
The fiber in black psyllium might reduce lithium absorption and plasma levels. Some case reports describe a reduction in plasma lithium levels with concomitant administration of blond psyllium. This was reversed when psyllium was stopped. This interaction may also occur with black psyllium.

Likelihood Probable Evidence D
Metformin (Glucophage)

Theoretically, black psyllium might increase the therapeutic and adverse effects of metformin.
Animal research shows that concurrent consumption of blond psyllium with metformin slows and increases the absorption of metformin. This interaction may also occur with black psyllium. To avoid changes in absorption, take psyllium 30-60 minutes after metformin.

Likelihood Possible Evidence D
Olanzapine (Zyprexa)

Theoretically, taking black psyllium at the same time as olanzapine might reduce olanzapine absorption.
The fiber in black psyllium might decrease the absorption of olanzapine. A single case report describes a reduction in the effectiveness of olanzapine when it was concomitantly administered with an unspecified type of psyllium 3 grams orally twice daily. This effect was reversed when psyllium was stopped.

Likelihood Possible Evidence D
Digoxin (Lanoxin)

Theoretically, taking black psyllium at the same time as digoxin might reduce digoxin absorption and decrease digoxin levels.
Psyllium might bind digoxin in the gut. However, some clinical evidence suggests that psyllium does not impact digoxin absorption.

Likelihood Unlikely Evidence B
Ethinyl Estradiol

Theoretically, taking black psyllium at the same time as ethinyl estradiol might alter levels of estradiol.
Concurrent use of blond psyllium with ethinyl estradiol results in a slight increase in the extent of ethinyl estradiol absorption and a slower rate of absorption. This is unlikely to be clinically significant.

Likelihood Unlikely Evidence D
Oral Drugs

Theoretically, psyllium might increase, decrease, or have no effect on the absorption of oral drugs.
Psyllium seems to have variable effects on drug absorption. To avoid changes in absorption, take psyllium 30-60 minutes after oral medications. Animal research shows that blond psyllium delays and increases the absorption of metformin and ethinyl estradiol. Case reports and animal research suggest that blond psyllium might reduce absorption of lithium, digoxin, olanzapine, and carbamazepine. Finally, some pharmacokinetic studies show that psyllium does not affect the absorption of levothyroxine or warfarin. Although many of these studies evaluated blond psyllium, the fiber content in black psyllium may have similar effects.

Likelihood Possible Evidence B
Plantain Leaf Extract full monograph & interactions

Kelp Whole Algae Extract9 drug types · 891 drugs

Amiodarone (Cordarone)

Theoretically, combining Fucus vesiculosus with amiodarone might cause excessively high iodine levels.
Fucus vesiculosus contains high concentrations of iodine. Amiodarone contains 37.3% iodine and can increase iodine levels. Concomitant use might increase the risk of having excessive iodine levels and adversely affecting thyroid function. Monitor thyroid function.

Likelihood Probable Evidence D
Antithyroid Drugs

Due to its iodine content, Fucus vesiculosus might alter the effects of antithyroid drugs.
Fucus vesiculosus contains high concentrations of iodine. Iodine in high doses has been reported to cause both hyperthyroidism and hypothyroidism, depending on the individual's past medical history. Taking Fucus vesiculosus while using antithyroid drugs could alter the effects of the antithyroid drugs.

Likelihood Possible Evidence D
Lithium

Concomitant use of Fucus vesiculosus and lithium has resulted in hyperthyroidism.
There is a case of hyperthyroidism occurring in a patient taking Fucus vesiculosus and lithium. Monitor thyroid hormones closely in patients taking lithium and Fucus vesiculosus concomitantly.

Likelihood Possible Evidence D
Thyroid Hormone

Due to its iodine content, Fucus vesiculosus might alter the effects of thyroid hormone.
Fucus vesiculosus contains high concentrations of iodine. Iodine in high doses has been reported to cause both hyperthyroidism and hypothyroidism, depending on the individual's past medical history. Taking Fucus vesiculosus while using thyroid hormone could alter the effects of thyroid hormone.

Likelihood Possible Evidence D
Anticoagulant/Antiplatelet Drugs

Theoretically, taking Fucus vesiculosus with antiplatelet or anticoagulant drugs might increase the risk of bruising and bleeding.
In vitro evidence suggests that a constituent of Fucus vesiculosus, known as fucoidan, has anticoagulant effects. However, in clinical research, fucoidan does not seem to have significant anticoagulant activity when taken orally, possibly due to poor absorption.

Likelihood Unlikely Evidence D
Cytochrome P450 2C8 (Cyp2C8) Substrates

Theoretically, concomitant use of Fucus vesiculosus with CYP2C8 substrates might increase the risk for adverse effects.
In vitro research shows that fucoidan, a constituent of Fucus vesiculosus, inhibits CYP2C8. This interaction has not been reported in humans.

Likelihood Possible Evidence D
Cytochrome P450 2C9 (Cyp2C9) Substrates

Theoretically, concomitant use of Fucus vesiculosus with CYP2C9 substrates might increase the risk for adverse effects.
In vitro research shows that fucoidan, a constituent of Fucus vesiculosus, inhibits CYP2C9. This interaction has not been reported in humans.

Likelihood Possible Evidence D
Cytochrome P450 2D6 (Cyp2D6) Substrates

Theoretically, concomitant use of Fucus vesiculosus with CYP2D6 substrates might alter the effects of these substrates.
In vitro research shows that fucoidan, a constituent of Fucus vesiculosus, both inhibits and induces CYP2D6. This interaction has not been reported in humans.

Likelihood Possible Evidence D
Cytochrome P450 3A4 (Cyp3A4) Substrates

Theoretically, concomitant use of Fucus vesiculosus with CYP3A4 substrates might increase the risk for adverse effects.
In vitro research shows that fucoidan, a constituent of Fucus vesiculosus, inhibits CYP3A4. This interaction has not been reported in humans.

Likelihood Possible Evidence D
Kelp Whole Algae Extract full monograph & interactions

Fennel Seed Extract6 drug types · 740 drugs

Anticoagulant/Antiplatelet Drugs

Theoretically, fennel might increase the risk of bleeding when used with antiplatelet or anticoagulant drugs.

Animal research suggests that fennel oil has antithrombotic and antiplatelet effects.

Likelihood Possible Evidence D
Ciprofloxacin (Cipro)

Theoretically, fennel might decrease the levels and clinical effects of ciprofloxacin.

Animal research shows that fennel reduces ciprofloxacin bioavailability by nearly 50%, possibly due to the metal cations such as calcium, iron, and magnesium contained in fennel. This study also found that fennel increased tissue distribution and slowed elimination of ciprofloxacin.

Likelihood Probable Evidence D
Contraceptive Drugs

Theoretically, taking large amounts of fennel might decrease the effects of contraceptive drugs due to competition for estrogen receptors.

Some constituents of fennel have estrogenic activity.

Likelihood Possible Evidence D
Cytochrome P450 3A4 (Cyp3A4) Substrates

Theoretically, fennel might increase levels of drugs metabolized by CYP3A4.

In vitro research suggests that fennel inhibits CYP3A4 enzyme activity. This effect has not been reported in humans.

Likelihood Possible Evidence D
Estrogens

Theoretically, taking large amounts of fennel might interfere with hormone replacement therapy due to competition for estrogen receptors.

Some constituents of fennel have estrogenic activity.

Likelihood Possible Evidence D
Tamoxifen (Nolvadex)

Theoretically, taking large amounts of fennel might decrease the antiestrogenic effect of tamoxifen.

Some constituents of fennel have estrogenic activity, which may interfere with the antiestrogenic activity of tamoxifen.

Likelihood Possible Evidence D
Fennel Seed Extract full monograph & interactions

Hawthorn Flower, Fruit, Leaf Extract6 drug types · 191 drugs

Nitrates

Theoretically, concomitant use might cause additive coronary vasodilatory effects.
Some evidence shows that hawthorn might lower blood pressure due to vasodilatory effects.

Likelihood Probable Evidence D
Phosphodiesterase-5 Inhibitors

Theoretically, concomitant use might result in additive vasodilation and hypotension.
Hawthorn might inhibit PDE-5 and cause vasodilation.

Likelihood Probable Evidence D
Anticoagulant/Antiplatelet Drugs

Theoretically, hawthorn may increase the risk of bleeding if used with anticoagulant or antiplatelet drugs.
In vitro and animal research shows that hawthorn can inhibit platelet aggregation. However, its effect in humans is unclear. One observational study shows that patients taking hawthorn shortly before undergoing coronary artery bypass graft (CABG) surgery or valve replacement surgery have a 10% incidence of postoperative bleeding, compared with 1% in those who never consumed hawthorn extract. However, clinical research shows that taking a specific preparation of dried hawthorn leaves and flowers (Crataesor, Soria Natural Lab) 800 mg three times daily for 15 days does not affect platelet aggregation or levels of thromboxane B2, the metabolite of thromboxane A2, in healthy humans.

Likelihood Possible Evidence D
Beta-Blockers

Theoretically, concomitant use might cause additive effects on blood pressure and heart rate.
Some evidence shows that hawthorn might lower blood pressure and heart rate.

Likelihood Possible Evidence D
Calcium Channel Blockers

Theoretically, concomitant use might cause additive coronary vasodilation and hypotensive effects.
Some evidence shows that hawthorn might lower blood pressure due to vasodilatory effects.

Likelihood Possible Evidence D
Digoxin (Lanoxin)

Theoretically, hawthorn might potentiate the effects and adverse effects of digoxin.
Hawthorn appears to improve cardiac output; however, hawthorn does not appear to affect digoxin pharmacokinetics. Case reports suggest that at least one species of hawthorn root extract (Crataegus mexicana) may produce adverse effects similar to digoxin and can cross-react with digoxin assays, leading to falsely elevated plasma digoxin levels.

Likelihood Possible Evidence D
Hawthorn Flower, Fruit, Leaf Extract full monograph & interactions

Burdock Root Extract1 drug type · 122 drugs

Anticoagulant/Antiplatelet Drugs

Theoretically, taking burdock with anticoagulant or antiplatelet drugs might increase the risk of bleeding.

In vitro research shows that lignans from burdock reduce rabbit platelet aggregation by inhibiting platelet activating factor. This interaction has not been reported in humans.

Likelihood Possible Evidence D
Burdock Root Extract full monograph & interactions
The maker

Brand information

Manufacturer and brand details for GF-G, from the product label.

Pure Herbs

See all Pure Herbs products
Name
Pure Herbs, Ltd.
City
Sterling Heights
State
MI
Phone Number
(800) 860-4372
Web Address
www.pureherbs.com
Pharmacist Counseling Corner

GF-G by Pure Herbs: Common Questions

Does GF-G by Pure Herbs interact with any medications?
Yes. Based on its ingredients, GF-G has a known interaction with 2,113 medications, including 14 rated major. Use the checker to see how it interacts with a specific drug.
How can one product interact with so many drugs?
GF-G contains 6 active ingredients, and an interaction can come from any of them. We check every ingredient, combine the results into one list per medication, and show which ingredient and mechanism is responsible.
Where does this information come from?
The product label data comes from the NIH Dietary Supplement Label Database (DSLD); the interaction data is built on the Natural Medicines database and reviewed by HelloPharmacist pharmacists.
Can I take this if I'm pregnant or breastfeeding?
No. The algae (kelp and bladderwrack) are rated possibly unsafe in pregnancy due to high iodine and possible heavy metal content, and iodine passes into breast milk and can harm your baby's thyroid. Fennel is also possibly unsafe in both pregnancy and lactation. Burdock and hawthorn don't have enough safety data for these times. Talk to your doctor or pharmacist about what's safe for you.
What is hawthorn supposed to do?
Hawthorn flower, fruit, and leaf have been used traditionally for heart and circulation support, but we don't have reliable evidence yet that it works for angina, arrhythmia, or other specific heart conditions. It does appear to lower blood pressure and heart rate in some studies, which is why it can interact with blood pressure medications.
Are the algae extracts safe to take long-term?
Long-term safety isn't well established. Kelp and bladderwrack have variable iodine levels that can disrupt your thyroid over time, and they may concentrate heavy metals from seawater. Because of this, the data rates them with caution for use.
Does plantain leaf extract really help with constipation?
Yes—plantain leaf extract (from black psyllium) is rated effective for constipation and likely effective for heart disease prevention. It works as a fiber. Just make sure you drink plenty of water with it to avoid blockages.
What common side effects should I expect?
The most common are digestive: bloating and gas from the plantain extract, and stomach upset from fennel in sensitive people. The algae can cause thyroid problems (goiter, overactive or underactive thyroid) if iodine levels are too high. Hawthorn is generally well tolerated, and burdock causes few side effects in food amounts, though allergic skin reactions have been reported with prolonged use.
Will this interact with my birth control?
Possibly. Fennel in this product has estrogenic activity and theoretically could decrease how well your birth control works. Talk to your pharmacist or doctor before adding this supplement to your regimen.

Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy

Not sure if GF-G is safe with your meds?

Our pharmacists answer your medication & supplement questions — free.

Ask a pharmacist

Label information is sourced from the NIH Dietary Supplement Label Database and reflects the product version on file; always read your actual product label. This page is for education only and is not a substitute for professional medical advice. Confirm with your pharmacist or doctor before combining supplements and medications.

GF-G label
Go deeper

The Full Monographs Behind GF-G’s Ingredients

Every ingredient we hold a full HelloPharmacist monograph for — uses, evidence, safety, and the complete interaction list.

Herb & supplement monograph

Fucus Vesiculosus

Interacts with 891 drugs

Fucus vesiculosus (bladderwrack) is a brown seaweed rich in iodine that has been used traditionally for thyroid concerns, weight, and skin. There is little solid human evidence to support mo...

Read the full Fucus Vesiculosus monograph → Herb & supplement monograph

Fennel

Interacts with 740 drugs

Fennel is a Mediterranean herb widely used as a food and spice, and traditionally taken for digestive complaints, colic, and menstrual cramps. Some small studies suggest possible benefit for...

Read the full Fennel monograph → Herb & supplement monograph

Burdock

Interacts with 122 drugs

Burdock is a traditional herb most often used for skin problems and as a so-called 'blood purifier,' but high-quality human studies are lacking and most claims are not well proven. It is wid...

Read the full Burdock monograph → Herb & supplement monograph

Black Psyllium

Interacts with 2,025 drugs

Black psyllium is a soluble-fiber supplement made from the seeds of a Plantago plant, used mostly to ease constipation and support digestive health. It is best known and most studied for rel...

Read the full Black Psyllium monograph → Herb & supplement monograph

Hawthorn

Interacts with 191 drugs

Hawthorn is a plant traditionally used for heart-related complaints, and some studies suggest it may modestly help symptoms of mild heart failure when added to standard care. However, the ev...

Read the full Hawthorn monograph →
Sources

Sources & How We Checked

GF-G's label data comes from the NIH Dietary Supplement Label Database; the ingredient interaction data is from the Natural Medicines database, reviewed by our pharmacists.

Content is written and reviewed by licensed HelloPharmacist pharmacists. See our data sources and editorial standards for how this information is built and checked.

The 86 references behind this product’s interaction data

Every citation that drives the interaction findings for this product’s ingredients, from the evidence-graded Natural Medicines (TRC Healthcare) database. Open an ingredient to browse its citations — links open the study on PubMed or the publisher’s site.

Fucus Vesiculosus 15 references
  1. Goodman GA, Rall TW, Nies AS, Taylor P. The Pharmacological Basis of Therapeutics, 9th ed.
  2. Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, DC: National Academy Press, 2002.
  3. Phaneuf D, Cote I, Dumas P, et al. Evaluation of the contamination of marine algae (Seaweed) from the St. Lawrence River and likely to be consumed by humans. Environ Res 1999;80:S175-S182. PubMed
  4. Durig J, Bruhn T, Zurborn KH, et al. Anticoagulant fucoidan fractions from Fucus vesiculosus induce platelet activation in vitro. Thromb Res 1997;85:479-91. PubMed
  5. Conz PA, La Greca G, Benedetti P, et al. Fucus vesiculosus: a nephrotoxic alga? Nephrol Dial Transplant 1998;13:526-7.
  6. Ohye H, Fukata S, Kanoh M, et al. Thyrotoxicosis caused by weight-reducing herbal medicines. Arch Intern Med 2005;165:831-4. PubMed
  7. Okamura K, Inoue K, Omae T. A case of Hashimoto's thyroiditis with thyroid immunological abnormality manifested after habitual ingestion of seaweed. Acta Endocrinol (Copenh) 1978;88:703-12. PubMed
  8. Agarwal SC, Crook JR, Pepper CB. Herbal remedies -- how safe are they? A case report of polymorphic ventricular tachycardia/ventricular fibrillation induced by herbal medication used for obesity. Int J Cardiol 2006;106:260-1. PubMed
  9. Sterling JB, Heymann WR. Potassium iodide in dermatology: a 19th century drug for the 21st century-uses, pharmacology, adverse effects, and contraindications. J Am Acad Dermatol 2000;43:691-7. PubMed
  10. Catania, M. A., Oteri, A., Caiello, P., Russo, A., Salvo, F., Giustini, E. S., Caputi, A. P., and Polimeni, G. Hemorrhagic cystitis induced by an herbal mixture. South.Med.J. 2010;103(1):90-92. PubMed
  11. Cumashi, A., Ushakova, N. A., Preobrazhenskaya, M. E., D'Incecco, A., Piccoli, A., Totani, L., Tinari, N., Morozevich, G. E., Berman, A. E., Bilan, M. I., Usov, A. I., Ustyuzhanina, N. E., Grachev, A. A., Sanderson, C. J., Kelly, M., Rabinovich, G. A., I
  12. Irhimeh, M. R., Fitton, J. H., and Lowenthal, R. M. Pilot clinical study to evaluate the anticoagulant activity of fucoidan. Blood Coagul.Fibrinolysis 2009;20(7):607-610. PubMed
  13. Arbaizar, B. and Llorca, J. [Fucus vesiculosus induced hyperthyroidism in a patient undergoing concomitant treatment with lithium]. Actas Esp.Psiquiatr. 2011;39(6):401-403.
  14. Church FC, Meade JB, Treanor RE, and et al. Antithrombin activity of fucoidan. The interaction of fucoidan with heparin cofactor II, antithrombin III, and thrombin. J Biol Chem 2-25-1989;264(6):3618-3623. DOI
  15. Mathew L, Burney M, Gaikwad A, et al. Preclinical evaluation of safety of fucoidan extracts from Undaria pinnatifida and Fucus vesiculosus for use in cancer treatment. Integr Cancer Ther 2017;16(4):572-84.

See these in context on the Fucus Vesiculosus monograph →

Fennel 17 references
  1. Leung AY, Foster S. Encyclopedia of Common Natural Ingredients Used in Food, Drugs and Cosmetics. 2nd ed. New York, NY: John Wiley & Sons, 1996.
  2. Brinker F. Herb Contraindications and Drug Interactions. 2nd ed. Sandy, OR: Eclectic Medical Publications, 1998.
  3. Zhu M, Wong PY, Li RC. Effect of oral administration of fennel (Foeniculum vulgare) on ciprofloxacin absorption and disposition in the rat. J Pharm Pharmacol 1999;51:1391-6.
  4. Gral N, Beani JC, Bonnot D, et al. [Plasma levels of psoralens after celery ingestion]. Ann Dermatol Venereol 1993;120:599-603.
  5. Burkhard PR, Burkhardt K, Haenggeli CA, Landis T. Plant-induced seizures: reappearance of an old problem. J Neurol 1999;246:667-70. PubMed
  6. Rosti L, Nardini A, Bettinelli ME, Rosti D. Toxic effects of a herbal tea mixture in two newborns. Acta Paediatrica 1994;83:683. PubMed
  7. Cuzzolin L, Zaffani S, and Benoni G. Safety implications regarding use of phytomedicines. Eur.J Clin Pharmacol. 2006;62:37-42. PubMed
  8. Tognolini, M., Ballabeni, V., Bertoni, S., Bruni, R., Impicciatore, M., and Barocelli, E. Protective effect of Foeniculum vulgare essential oil and anethole in an experimental model of thrombosis. Pharmacol.Res 2007;56(3):254-260. PubMed
  9. Subehan, Usia, T., Iwata, H., Kadota, S., and Tezuka, Y. Mechanism-based inhibition of CYP3A4 and CYP2D6 by Indonesian medicinal plants. J Ethnopharmacol. 5-24-2006;105(3):449-455. PubMed
  10. Tognolini, M., Barocelli, E., Ballabeni, V., Bruni, R., Bianchi, A., Chiavarini, M., and Impicciatore, M. Comparative screening of plant essential oils: phenylpropanoid moiety as basic core for antiplatelet activity. Life Sci. 2-23-2006;78(13):1419-1432. PubMed
  11. Subehan, Zaidi, S. F., Kadota, S., and Tezuka, Y. Inhibition on human liver cytochrome P450 3A4 by constituents of fennel (Foeniculum vulgare): identification and characterization of a mechanism-based inactivator. J Agric.Food Chem. 12-12-2007;55(25):101 PubMed
  12. LEVY, S. B. Bronchial asthma due to ingestion of fennel and fennel seed. Ann.Allergy 1948;6(4):415.
  13. Ottolenghi, A., De Chiara, A., Arrigoni, S., Terracciano, L., and De Amici, M. [Diagnosis of food allergy caused by fruit and vegetables in children with atopic dermatitis]. Pediatr Med Chir 1995;17(6):525-530.
  14. Trabace L, Tucci P, Ciuffreda L, et al. "Natural" relief of pregnancy-related symptoms and neonatal outcomes: above all do no harm. J Ethnopharmacol. 2015;174:396-402. PubMed
  15. Denaxa D, Arkwright PD. Fennel as a cause of immediate hypersensitivity to toothpaste. Ann Allergy Asthma Immunol. 2020;125(1):99-100. PubMed
  16. Lee HW, Ang L, Lee MS, Alimoradi Z, Kim E. Fennel for reducing pain in primary dysmenorrhea: a systematic review and meta-analysis of randomized controlled trials. Nutrients 2020;12(11):3438. PubMed
  17. Mathew T, John SK, Javali M, Vasireddy M, Nadig R, Sarma GRK. Substance use related cluster headache: A case series. Headache 2022;62(7):908-910. PubMed

See these in context on the Fennel monograph →

Burdock 11 references
  1. Iwakami S, Wu JB, Ebizuka Y, Sankawa U. Platelet activating factor (PAF) antagonists contained in medicinal plants: lignans and sesquiterpenes. Chem Pharm Bull (Tokyo) 1992;40:1196-8. PubMed
  2. Sasaki Y, Kimura Y, Tsunoda T, Tagami H. Anaphylaxis due to burdock. Int J Dermatol 2003;42:472-3. PubMed
  3. Rhoads PM, Tong TG, Banner W Jr, Anderson R. Anticholinergic poisonings associated with commercial burdock root tea. J Toxicol Clin Toxicol 1984-85;22:581-4. PubMed
  4. Rodriguez P, Blanco J, Juste S, et al. Allergic contact dermatitis due to burdock (Arctium lappa). Contact Dermatitis 1995;33:134-5.
  5. Kassler, W. J., Blanc, P., and Greenblatt, R. The use of medicinal herbs by human immunodeficiency virus-infected patients. Arch Intern Med 1991;151(11):2281-2288. DOI
  6. Chan, Y. S., Cheng, L. N., Wu, J. H., Chan, E., Kwan, Y. W., Lee, S. M., Leung, G. P., Yu, P. H., and Chan, S. W. A review of the pharmacological effects of Arctium lappa (burdock). Inflammopharmacology. 2011;19(5):245-254. PubMed
  7. Breed, F. B. and Kuwabara, T. Burdock ophthalmia. Arch Ophthalmol 1966;75(1):16-20.
  8. Bryson, P. D., Watanabe, A. S., Rumack, B. H., and Murphy, R. C. Burdock root tea poisoning. Case report involving a commercial preparation. JAMA 5-19-1978;239(20):2157. DOI
  9. <p>Fletcher GF<span>, </span>Cantwell JD. Burdock root tea poisoning. JAMA <span>1978 Oct 6;240(15):1586.</span></p> DOI
  10. Latif A, Fichadiya H, Abid F, Capo G. Herbal Teas and Thrombocytopenia: A Curious Case of Yellow Dock and Burdock-Induced Thrombocytopenia. Eur J Case Rep Intern Med 2022;9(3):003247. PubMed
  11. Niazi B, Ahmed K, Ahmed M, Ali S, Song K, Elias S. Drug-Induced Liver Injury from Herbal Liver Detoxification Tea. Case Rep Gastroenterol 2022;16(3):612-617. PubMed

See these in context on the Burdock monograph →

Black Psyllium 18 references
  1. McGuffin M, Hobbs C, Upton R, Goldberg A, eds. American Herbal Products Association's Botanical Safety Handbook. Boca Raton, FL: CRC Press, LLC 1997.
  2. Gruenwald J, Brendler T, Jaenicke C. PDR for Herbal Medicines. 1st ed. Montvale, NJ: Medical Economics Company, Inc., 1998.
  3. Covington TR, et al. Handbook of Nonprescription Drugs. 11th ed. Washington, DC: American Pharmaceutical Association, 1996.
  4. Etman M. Effect of a bulk forming laxative on the bioavailablility of carbamazepine in man. Drug Dev Ind Pharm 1995;21:1901-6.
  5. Perlman BB. Interaction between lithium salts and ispaghula husk. Lancet 1990;335:416.
  6. Vaswani SK, Hamilton RG, Valentine MD, Adkinson NF. Psyllium laxative-induced anaphylaxis, asthma, and rhinitis. Allergy 1996;51:266-8. PubMed
  7. Lantner RR, Espiritu BR, Zumerchik P, Tobin MC. Anaphylaxis following ingestion of a psyllium-containing cereal. JAMA 1990;264:2534-6. DOI
  8. Kaplan MJ. Anaphylactic reaction to "Heartwise." N Engl J Med 1990;323:1072-3. DOI
  9. Nordstrom M, Melander A, Robertsson E, Steen B. Influence of wheat bran and of a bulk-forming ispaghula cathartic on the bioavailability of digoxin in geriatric in-patients. Drug Nutr Interact 1987;5:67-9..
  10. Robinson DS, Benjamin DM, McCormack JJ. Interaction of warfarin and nonsystemic gastrointestinal drugs. Clin Pharmacol Ther 1971;12:491-5. PubMed
  11. Garcia JJ, Fernandez N, Diez MJ, et al. Influence of two dietary fibers in the oral bioavailability and other pharmacokinetic parameters of ethinyloestradiol. Contraception 2000;62:253-7. PubMed
  12. Fernandez N, Lopez C, Díez R, et al. Drug interactions with the dietary fiber Plantago ovata husk. Expert Opin Drug Metab Toxicol 2012;8(11):1377-86.
  13. Semen plantaginis in: WHO Monographs on Selected Medicinal Plants, volume 1. World Health Organization, Geneva, 1999. Available at http://apps.who.int/medicinedocs/en/d/Js2200e/. Accessed November 26, 1026.
  14. Code of Federal Regulations, Title 21 (21CFR 101.17). Food labeling warning, notice, and safe handling statements. Available at www.ecfr.gov/cgi-bin/text-idx?SID=20f647d3b74161501f46564b915b4048&mc=true&node=se21.2.101_117&rgn=div8. Accessed December 3, 2
  15. Code of Federal Regulations, Title 21 (21CFR 201.319). Specific labeling requirements - water-soluble gums, hydrophilic gums, and hydrophilic mucilloids. Available at www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?fr=201.319. Accessed Dece
  16. Diez R, Garcia JJ, Diez MJ, Sierra M, Sahagun AM, Fernandez N. Influence of Plantago ovata husk (dietary fiber) on the bioavailability and other pharmacokinetic parameters of metformin in diabetic rabbits. BMC Complement Altern Med. 2017 Jun 7;17(1):298. PubMed
  17. Chiu AC, Sherman SI. Effects of pharmacological fiber supplements on levothyroxine absorption. Thyroid. 1998;8(8):667-71. PubMed
  18. Merrick C, Madden CA, Capurso NA. A Case of Blunted Orally Disintegrating Olanzapine Effect Due to Coadministered Psyllium. J Clin Psychiatry 2021;82(2):20cr13633. PubMed

See these in context on the Black Psyllium monograph →

Hawthorn 25 references
  1. Tauchert M. Efficacy and safety of crataegus extract WS 1442 in comparison with placebo in patients with chronic stable New York Heart Association class-III heart failure. Am Heart J 2002;143:910-5. PubMed
  2. Pittler MH, Schmidt K, Ernst E. Hawthorn extract for treating chronic heart failure: meta-analysis of randomized trials. Am J Med 2003;114:665-74.. PubMed
  3. Chang Q, Zuo Z, Harrison F, Chow MS. Hawthorn. J Clin Pharmacol 2002;42:605-12.
  4. Holubarsch CJ, Colucci WS, Meinertz T, et al. The efficacy and safety of Crataegus extract WS 1442 in patients with heart failure: the SPICE trial. Eur J Heart Fail 2008;10:1255-63. PubMed
  5. Pittler MH, Guo R, and Ernst E. Hawthorn extract for treating chronic heart failure. Cochrane.Database.Syst Rev 2008:CD005312. PubMed
  6. Zick SM, Vautaw BM, Gillespie B, Aaronson KD. Hawthorn Extract Randomized Blinded Chronic Heart Failure (HERB CHF) trial. Eur J Heart Fail. 2009;11:990-99. PubMed
  7. Werner NS, Duschek S, and Schandry R. D-camphor-crataegus berry extract combination increases blood pressure and cognitive functioning in the elderly - a randomized, placebo controlled double blind study. Phytomedicine. 2009;16:1077-82. PubMed
  8. Dalli E, Colomer E, Tormos MC, et al. Crataegus laevigata decreases neutrophil elastase and has hypolipidemic effect: a randomized, double-blind, placebo-controlled trial. Phytomedicine. 6-15-2011;18:769-75. PubMed
  9. Maek-a-nantawat W, Phonrat B, Dhitavat J, et al. Safety and efficacy of CKBM-A01, a Chinese herbal medicine, among asymptomatic HIV patients. Southeast Asian J Trop.Med Public Health 2009;40:494-501.
  10. Asher GN, Viera AJ, Weaver MA, et al. Effect of hawthorn standardized extract on flow mediated dilation in prehypertensive and mildly hypertensive adults: a randomized, controlled cross-over trial. BMC.Complement Altern.Med 2012;12:26. PubMed
  11. Walker AF, Marakis G, Simpson E, et al. Hypotensive effects of hawthorn for patients with diabetes taking prescription drugs: a randomised controlled trial. Br J Gen.Pract 2006;56:437-43.
  12. Daniele C, Mazzanti G, Pittler MH, et al. Adverse-event profile of Crataegus spp.: a systematic review. Drug Saf 2006;29:523-35. PubMed
  13. Tankanow R, Tamer HR, Streetman DS, et al. Interaction study between digoxin and a preparation of hawthorn (Crataegus oxyacantha). J.Clin.Pharmacol. 2003;43:637-42. DOI
  14. Tauchert, M., Gildor, A., and Lipinski, J. [High-dose Crataegus extract WS 1442 in the treatment of NYHA stage II heart failure]. Herz 1999;24(6):465-474.
  15. Horoz, M., Gok, E., Genctoy, G., Ozcan, T., Olmaz, R., Akca, M., Kiykim, A., and Gurses, I. Crataegus orientalis associated multiorgan hypersensitivity reaction and acute renal failure. Intern.Med 2008;47(23):2039-2042. PubMed
  16. Dalli, E., Valles, J., Cosin-Sales, J., Santos, M. T., Moscardo, A., Milara, J., and Sotillo, J. F. Effects of hawthorn (Crataegus laevigata) on platelet aggregation in healthy volunteers. Thromb.Res 2011;128(4):398-400. PubMed
  17. Rogov VD. [Toxiderma due to the fruits of the hawthorn]. Vestn Dermatol Venerol 1984;7(7):46-47.
  18. Loew D, Albrecht M, and Podzuweit H. Efficacy and tolerability of a Hawthorn preparation in patients with heart failure Stage I and II according to NYHA - a surveillance study. Phytomedicine 1996;3(Suppl 1):92.
  19. Rababa'h AM, Altarabsheh SE, Haddad O, Deo SV, Obeidat Y, Al-Azzam S. Hawthorn Herb Increases the Risk of Bleeding after Cardiac Surgery: An Evidence-Based Approach. Heart Surg Forum 2016;19(4):E175-9. PubMed
  20. Shatoor AS, Soliman H, Al-Hashem F, Gamal BE, Othman A, El-Menshaw N. Effect of hawthorn (Crataegus aronia syn. Azarolus (L)) on platelet function in albino wistar rats. Thromb Res 2012;130(1):75-80. PubMed
  21. Vibes J, Lasserre B, Gleye J, Declume C. Inhibition of thromboxane A2 biosynthesis in vitro by the main components of Crataegus oxyacantha (hawthorn) flower heads. Prostaglandins Leukot Essent Fatty Acids 1994;50(4):173-5. PubMed
  22. Rogers KL, Grice ID, Griffiths LR. Inhibition of platelet aggregation and 5-HT release by extracts of Australian plants used traditionally as headache treatments. Eur J Pharm Sci 2000;9(4):355-63. PubMed
  23. Zhou CC, Huang XX, Gao PY, et al. Two new compounds from Crataegus pinnatifida and their antithrombotic activities. J Asian Nat Prod Res 2014;16(2):169-74.
  24. Palmer KG, Lebin JA, Cronin MT, Mazor SS, Burns RA. Crataegus mexicana (Tejocote) Exposure Associated with Cardiotoxicity and a Falsely Elevated Digoxin Level. J Med Toxicol. 2019;15(4):295-298. PubMed
  25. Espinosa J, Bassett R, Lucerna A, Finn D. Hawthorne root (Crataegus mexicana) toxicity. Am J Emerg Med. 2024;78:242.e5-242.e6. PubMed

See these in context on the Hawthorn monograph →

Parts of this content are provided by the Therapeutic Research Center, LLC.

DISCLAIMER: Currently this does not check for drug-drug interactions. This is not an all-inclusive comprehensive list of potential interactions and is for informational purposes only. Not all interactions are known or well-reported in the scientific literature, and new interactions are continually being reported. Input is needed from a qualified healthcare provider including a pharmacist before starting any therapy. Application of clinical judgment is necessary.

© 2021 Therapeutic Research Center, LLC

Keep exploring
Supplement interaction checker › Check any supplement or product against your medications Drug–drug interactions › Check two or more of your medications against each other Browse medications A–Z › Every drug we've checked against herbs & supplements NDC & pricing lookup › Find a drug’s NDCs, packaging and costs Ask a pharmacist › Free, personal answer from our licensed team