Herb & supplement monograph

Collard Drug Interactions, Uses, Effectiveness, Safety & More

Medically reviewed by Dr. Brian Staiger, PharmD, BCPS ·Updated June 2026

What is this page for?

First and foremost: how Collard interacts with medications. The heart of this page is the interaction list — every drug Collard is known to interact with, and how serious each one is.

But these pages have grown well beyond that into a full monograph — what Collard is, what people use it for and how strong the evidence is, its safety and side effects, and answers to the questions we’re asked most — written and reviewed by the clinical staff at HelloPharmacist. It’s educational information from our licensed clinical databases, not medical advice, and we don’t sell or endorse products. Our editorial policy

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Interaction report

Drugs that interact with Collard

86 medications have a known interaction with Collard, graded by severity. Select any drug for the full evidence-based detail.

Don’t want to scroll the list? Just ask.

Tell us the medications you take and we’ll check each one against Collard using our pharmacist-reviewed interaction data.

AI summaries are generated from our Collard interaction data for education only — always confirm with your pharmacist. How we use AI

2,830 drugs

Read The List Like a Pharmacist

What Severity, Likelihood & Evidence Mean

Severity — How Serious It Can Be

Major. Clinically significant; generally best avoided, or used only under direct professional supervision.
Moderate. May need monitoring, a dose adjustment, or separating the times you take each one.
Minor. Generally not clinically significant, but still worth noting and mentioning to your pharmacist.
No known interaction. Checked against our sources with nothing documented — not the same as proven safety.

Likelihood — How Well It’s Documented

Likely. Well-controlled human studies have demonstrated the likely existence of this interaction
Probable. Interaction has not been documented in well-controlled studies, however, the interaction has been demonstrated in some small human studies or in controlled animal studies in conjunction with multiple case reports.
Possible. Interaction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists
Unlikely. Interaction has been demonstrated in animal or in lab research but has been shown not to occur in humans.

Where This Data Comes From

Interaction records are evidence-graded and sourced from the Natural Medicines database (TRC Healthcare), the same reference used by pharmacists and hospitals.
Each drug listed above links to the full report for that exact Collard combination — clinical detail, likelihood, evidence level, and citations.
Content is reviewed by licensed HelloPharmacist pharmacists — see our data sources and editorial standards.

The big picture

The kinds of drugs Collard affects

Every type of medication (drug category) Collard is known to interact with. Open any category for the detail — or search your exact drug in the checker above.

All 1 drug category Collard interacts with

Antidiabetes Drugs

In an animal study, an aqueous extract of collard leaves and stems has been shown to reduce glucose levels. Collard extract 60 mg/kg lowers blood glucose levels in a rat model of diabetes after both single- and multi-dose oral administration similarly to glibenclamide 5 mg/kg. Theoretically, collard extract might have additive effects when used concomitantly with antidiabetes drugs and may increase the risk of hypoglycemia. Monitor blood glucose levels closely. Dose adjustments may be necessary. Some antidiabetes drugs include glimepiride (Amaryl), glyburide (DiaBeta, Glynase PresTab, Micronase), insulin, pioglitazone (Actos), rosiglitazone (Avandia), chlorpropamide (Diabinese), glipizide (Glucotrol), and tolbutamide (Orinase).

Likelihood Possible Evidence D

Monograph

Collard: Uses, Safety & Side Effects

Medically reviewed by Dr. Brian Staiger, PharmD, BCPS · Reviewed June 2026 ·

The bottom line

Collard is a leafy green vegetable in the cabbage family that is rich in vitamins, minerals, and fiber, and is best thought of as a nutritious food rather than a medicine. Eating it as part of a balanced diet is healthy for most people, but there is little high-quality research on collard as a concentrated supplement. If you take blood thinners or have kidney concerns, talk with your pharmacist or doctor because of its vitamin K and oxalate content.

Scientific name: Brassica oleracea var. viridis
Family: Brassicaceae
Part used: Leaves
Common forms: Fresh or cooked leaves, frozen greens; occasionally powders or capsules

People commonly use it for

General nutrition and vitamin source
Bone health
Heart health support
Digestive fiber
Antioxidant intake

Popular and traditional uses — not proof it works. See “Uses & effectiveness” below for the evidence.

Safety at a glance

OverallLikely safe

Collard is widely eaten as a food and is generally safe for most people.

PregnancyInsufficient reliable information

Insufficient reliable information available; avoid amounts in excess of those found in foods.

Read the full pregnancy detail

BreastfeedingInsufficient reliable information

Insufficient reliable information available; avoid amounts in excess of those found in foods.

Read the full breastfeeding detail

Pregnancy & breastfeeding ratings are from Natural Medicines (Therapeutic Research Center). Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

Jump to a section

Overview

Collard (often called collard greens) is a leafy green vegetable in the cabbage and broccoli family. It comes from the plant Brassica oleracea, the same species that gives us kale, cabbage, and broccoli. Collard has large, smooth, dark-green leaves and is grown widely in warm and temperate regions, including the southern United States, where it is a popular food.

Most people use collard as a food rather than as a supplement. The leaves are usually cooked, steamed, sautéed, or added to soups and stews. Collard is valued for being rich in vitamins, minerals, and fiber while being low in calories.

How it works

Collard contains several compounds that may support health. It is high in fiber, which aids digestion and helps with regularity. It provides vitamin K, which is needed for blood clotting and bone health, and vitamin C and carotenoids that act as antioxidants.

Like other cabbage-family vegetables, collard contains glucosinolates, natural plant compounds that the body can convert into substances such as sulforaphane. Laboratory and animal studies suggest these compounds may have antioxidant and protective effects, but this research is early and does not prove that eating collard prevents or treats any disease in people.

Effectiveness

Does Collard work?

Here’s what the research actually shows for each use — graded by Natural Medicines and reviewed by Dr. Brian Staiger, PharmD.

Evidence overview · 3 uses evaluated

3 Insufficient evidence

How to read these evidence grades

Natural Medicines’ 7-point scale. We show each rating’s label word-for-word.

1EffectiveStrong, consistent evidence it works.

2Likely EffectiveGood evidence, though not yet conclusive.

3Possibly EffectiveSome evidence suggests a benefit.

4Possibly IneffectiveSome evidence it may not help.

5Likely IneffectiveFairly strong evidence it doesn’t help.

6IneffectiveStrong evidence it doesn’t work.

7Insufficient Reliable Evidence to RateToo little research to say either way.

For Collard, current evidence isn’t strong enough to rate any specific use. The conditions it has been studied for are listed below.

Also studied for 3 conditions — evidence insufficient to rate

Insufficient Reliable Evidence To Rate Bladder cancer

Rating & evidence shown verbatim from Natural Medicines

Observational research has found that eating about 0.88 cups of cruciferous vegetables, such as cabbage, Brussels sprout, cauliflower, broccoli, kale, or collards, decreases the risk of developing bladder cancer by about 30% in men and women.

Sources Ref 14864

Insufficient Reliable Evidence To Rate Breast cancer

Rating & evidence shown verbatim from Natural Medicines

Population research has found that higher intake of cruciferous vegetables, including broccoli, Brussels sprout, cabbage, cauliflower, collards, and kale, is associated with a slight increase in the risk of breast cancer in premenopausal women, while higher intake of cruciferous vegetables appears to be associated with a slight but statistically insignificant decrease in the risk of breast cancer in postmenopausal women.

Sources Ref 26188

Insufficient Reliable Evidence To Rate Prostate cancer

Rating & evidence shown verbatim from Natural Medicines

Population research has found that people who consume higher amounts of green leafy vegetables, such as collard, spinach, mustard greens, and turnip greens, do not have a significantly lower risk of developing prostate cancer when compared with those who eat lower amounts.

Sources Ref 25420

Source & disclaimer. Effectiveness ratings and evidence summaries are provided by Natural Medicines (Therapeutic Research Center) and shown as licensed. Where Natural Medicines hasn’t rated a use, HelloPharmacist’s pharmacists may add their own reviewed rating and evidence (each such entry is labeled). This is educational information, not medical advice — talk with your pharmacist or doctor before starting, stopping, or changing a supplement.

Safety & precautions

As a food, collard is safe for most people and is a healthy part of a balanced diet, including during pregnancy and breastfeeding. Wash the leaves well and cook them properly to reduce the risk of foodborne illness.

A few groups should be more careful. People taking blood-thinning medications should keep their intake of vitamin K–rich greens steady rather than suddenly eating much more or less, and should discuss this with their pharmacist or doctor. People with kidney stones or kidney disease may need to limit collard because it contains oxalates and potassium. Those with thyroid conditions should know that very large amounts of raw cabbage-family vegetables contain goitrogens, though normal cooked portions are not usually a concern.

Side effects

Collard is generally well tolerated. The most common complaints are gas, bloating, or stomach discomfort, especially when eaten in large amounts, because of its fiber and natural plant compounds.

Serious problems are uncommon. People prone to kidney stones may be affected by its oxalate content over time. As with any food, an allergic reaction is possible but rare. Concentrated supplement forms have not been well studied for safety, so it is best to get collard from food.

Dosing

There is no established medicinal dose for collard. As a food, it can be enjoyed in normal serving sizes as part of a varied diet, just like other vegetables.

If you choose a collard powder or capsule, there is no standardized dose, so follow the directions on the product label. Talk with your pharmacist or doctor before using concentrated supplements, especially if you take medications or have kidney or thyroid problems.

Pregnancy & Breastfeeding

Collard & Pregnancy

Insufficient reliable information

Insufficient reliable information available; avoid amounts in excess of those found in foods.

Collard & Breastfeeding

Insufficient reliable information

Insufficient reliable information available; avoid amounts in excess of those found in foods.

DISCLAIMER: This tool is intended for informational purposes only, and should not be interpreted as specific medical advice. Patients should consult with a qualified healthcare provider before making decisions about therapies and/or health conditions.

© 2026 Therapeutic Research Center

Pregnancy & lactation ratings: Natural Medicines, Therapeutic Research Center

References & further reading

The 4 references that drive our Collard monograph and interaction data, from the evidence-graded Natural Medicines (TRC Healthcare) database. Citations with a link open the study on PubMed or the publisher’s site.

Zhao H, Lin J, Grossman HB, et al. Dietary isothiocyanates, GSTM1, GSTT1, NAT2 polymorphisms and bladder cancer risk. Int J Cancer 2007;120:2208-13.
Cohen, J. H., Kristal, A. R., and Stanford, J. L. Fruit and vegetable intakes and prostate cancer risk. J Natl.Cancer Inst. 1-5-2000;92(1):61-68. PubMed
Gaudet MM, Britton JA, Kabat GC, et al. Fruits, vegetables, and micronutrients in relation to breast cancer modified by menopause and hormone receptor status. Cancer Epidemiol Biomarkers Prev 2004;13(9):1485-94. DOI
Amssayef A, Eddouks M. Antihyperglycemic Effect of the Moroccan Collard Green (Brassica oleracea var. viridis) in Streptozotocin-Induced Diabetic Rats. Endocr Metab Immune Disord Drug Targets 2020. PubMed

Keep reading

This information is for education only and is not a substitute for professional medical advice. Always check with your pharmacist or doctor before starting, stopping, or combining supplements and medications.

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.

Brand directory

Brands that make products with Collard

91 brands in our database make a supplement containing Collard.

Advanced Nutrition by Zahler 135 products Akasha Naturals 20 products Applied Nutrition 76 products Bare Performance Nutrition 12 products Beast Sports Nutrition 23 products Body Ecology 37 products Catie's 23 products Controlled Labs 29 products Country Farms 76 products Country Life 1,501 products Country Life Realfood Organics 39 products CTD Sports 1 product Daily Nutrition 14 products Designed by Dean 10 products Designs for Health 295 products Detox Organics 1 product Divine Health 56 products doTERRA 208 products Douglas Laboratories 3,067 products Dr. Berg 106 products Dr. Berg's 16 products Dr. Mercola 590 products DrBerg Nutritionals 10 products DrVita.com 1 product

Product directory

Supplement products with Collard

401 products in our database contain Collard. Open any to see its full ingredient list and every drug interaction we check.

Pharmacist Counseling Corner

Collard: Common Questions

What is Collard used for, and does it work?

People use Collard for a range of reasons, but according to the Natural Medicines database the current clinical evidence is insufficient to confirm it works for the specific conditions it has been studied for. See the graded list on this page, and talk to your pharmacist or doctor before relying on it for any condition.

Does Collard interact with prescription medications?

Yes. We list 86 medications with a known interaction with Collard. Use the checker above to see how Collard interacts with a specific drug.

How are Collard interactions rated?

Each interaction is graded major, moderate, or minor based on how clinically significant it is and the strength of the evidence behind it. Major interactions are the most serious and are best avoided, or used only under close professional supervision.

Is it safe to take Collard with my medications?

It depends on the specific medication. Some combinations are fine, while others call for monitoring, timing changes, or should be avoided. Check your exact drug above and confirm with your pharmacist or doctor before starting, stopping, or changing anything.

Where does this Collard interaction information come from?

Our interaction data is built on the Natural Medicines database — an evidence-graded reference for vitamins, herbs, and supplements — and is reviewed by licensed HelloPharmacist pharmacists, who may add clinical context.

Is Collard a medicine or a food?

Collard is best thought of as a nutritious vegetable, not a medicine. It provides vitamins, minerals, and fiber, but there is little research supporting it as a treatment for specific conditions.

Is it safe to eat Collard during pregnancy?

Yes, eating Collard in normal food amounts is generally safe and even beneficial during pregnancy because it provides folate, vitamins, and fiber. Wash and cook it well, and ask your doctor before using concentrated supplements.

Can Collard cause kidney stones?

Collard contains oxalates, which in large amounts may contribute to kidney stones in people who are prone to them. If you have a history of kidney stones, ask your doctor how much is appropriate for you.

Should I eat Collard raw or cooked?

Both are fine, but Collard is usually cooked, which makes the tough leaves easier to digest and may reduce the effect of natural goitrogens. Cooking also helps reduce the risk of foodborne germs.

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

Keep exploring

Products that contain Collard

A rotating sample of real supplements in our database that list Collard — open any to see its full ingredients and every drug interaction we check.

See all 401 products with Collard →

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Collard Drug Interactions, Uses, Effectiveness, Safety & More

Your Choice:

Drugs that interact with Collard

Don’t want to scroll the list? Just ask.

What Severity, Likelihood & Evidence Mean

Severity — How Serious It Can Be

Likelihood — How Well It’s Documented

Where This Data Comes From

The kinds of drugs Collard affects

Collard: Uses, Safety & Side Effects

Overview

How it works

Does Collard work?

Safety & precautions

Side effects

Dosing

Collard & Pregnancy

Collard & Breastfeeding

References & further reading

Brands that make products with Collard

Supplement products with Collard

Collard: Common Questions

Related supplements & herbs

Products that contain Collard

Have a question about Collard?