Interactions on record — worth a quick check against your medications. Based on 1 of 2 ingredients. Check your meds →
Dietary supplement

Castor Oil 650 mg Ingredients & Drug Interactions

by NOW

Castor Oil 650 mg label
See full label image
Softgel Capsule Category: Fat/fatty Acid
Most serious interaction: Moderate
Clinical methodology reviewed by · Updated Sep 16, 2026 · Label data from the NIH DSLD
What is this page for?

First and foremost: checking Castor Oil 650 mg 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: Moderate

Castor Oil 650 mg is a dietary supplement by NOW with 2 active ingredients. Its ingredients are commonly taken for digestive upset and bloating, infant colic, menstrual cramps.Based on those ingredients, 740 medications have a known interaction with it, the most serious rated moderate. The ingredients most likely to interact are Fennel oil. Use the checker below to test your specific medication, or read the full HelloPharmacist Interaction Report.

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Check Your Meds Against Castor Oil 650 mg by NOW

Ask about any prescription or over-the-counter medication and we check it for interactions with Castor Oil 650 mg by NOW — and tell you which ingredient is responsible.

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HelloPharmacist Scorecard of Castor Oil 650 mg by NOW

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 12, 2026

What’s inside

Full disclosure
Ingredient Transparency · database check
Full

Every active ingredient lists its own amount on the label.

Why this rating?
  • The label discloses an exact amount for 2 of its 2 active ingredients.
  • No proprietary blends here — you can verify the dose of every single component.

This softgel delivers 2 active ingredients: fennel oil and castor oil. Fennel oil is the component with documented effects in our data; castor oil makes up the bulk of the formula but we have no interaction or safety information on file for it.

The capsule itself is the inactive ingredient.

Does it work?

Insufficient evidence
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
Insufficient

There isn't enough reliable clinical evidence to rate this product's ingredients for its stated purpose.

Why this rating?
  • The label markets this product for: relief of occasional constipation.
  • We looked for evidence on: Constipation.
  • The closest evidence on file: Fennel is rated "Insufficient Reliable Evidence To Rate" for Constipation (Natural Medicines).

Fennel oil is possibly effective for dysmenorrhea (painful periods). For anxiety, bronchitis, nocturnal enuresis (bedwetting), and cholera, the evidence we hold is insufficient to rate whether it works.

This product is primarily fennel oil, so effectiveness would depend on that ingredient's activity.

The evidence, ingredient by ingredient Fennel

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 1 of the 1 matched ingredient.
  • Pregnancy & breastfeeding safety ratings cover 1 of 1.
  • General safety write-ups exist for 1 of 1.
  • Remember: this measures how much safety information exists. Thin data is not the same as being safe.

Fennel oil is generally well tolerated when taken by mouth, though some people report gastrointestinal discomfort, sun sensitivity (photosensitivity), or allergic reactions — rarely, seizures have been reported. Allergic reactions can include breathing difficulty and wheezing.

The safety data advises against medicinal or concentrated amounts during pregnancy because of limited safety data and possible hormone-like effects. While breastfeeding, food amounts are likely fine, but medicinal doses are not well studied — talk with your doctor or pharmacist for personalized advice.

Side effects, ingredient by ingredient Fennel

Meds to double-check

Moderate interaction found
Known Interaction Concern · database check
Moderate identified

The most serious documented interaction for these ingredients is Moderate. Check your medications for a personalized result.

Why this rating?
  • 1 of the 1 matched ingredient can interact with medications — Fennel.
  • The most serious interaction on file is rated Moderate.
  • Some involve high-stakes drug classes: anticoagulant / antiplatelet drugs.
  • For scale: 741 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.

Check with your pharmacist if you take blood thinners or antiplatelet drugs (Moderate risk of bleeding), birth control pills or hormone replacement therapy (Moderate risk of reduced effect), the antibiotic ciprofloxacin (Moderate risk of reduced antibiotic strength), tamoxifen (Moderate risk of reduced cancer drug effect), or any medications processed by the liver enzyme CYP3A4 (Moderate risk of raised drug levels).

Check your own medication Run your meds through the checker above

The bottom line

Scorecard at a glanceFully disclosed formula with insufficient evidence for its stated purpose. Moderate medication interactions have been identified, and safety information is well characterized.

This product is an option if you're looking for a fennel oil supplement and have no drug interactions with it. If you take any blood thinner, birth control, hormone therapy, ciprofloxacin, tamoxifen, or medications metabolized by CYP3A4, check your exact drugs here first.

Pregnant or breastfeeding? Run it past your pharmacist or doctor before starting.

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

Assessment coverage: 1 of 2 active ingredients matched to our full ingredient reviews (monographs). Based on the product label dated Apr 25, 2017.

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 Castor Oil 650 mg, straight from the product label.

Brand NOW
Barcode (UPC) 733739017239
Net contents 120 Softgel(s)
Market status On market
Date entered into DSLD Apr 25, 2017
DSLD ID 73568
Product type Fat/fatty Acid
Supplement form Softgel Capsule
Dietary claims / uses Nutrient, All Other, Structure/Function
Intended target group(s) Adult (18 - 50 Years), Gluten Free, Dairy Free
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 Castor Oil 650 mg by NOW, 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:
1 Softgel(s)
Maximum serving Sizes:
1 Softgel(s)
UPC/BARCODE
733739017239
IngredientAmount% DV
Calories5 Calorie(s)--
Total Fat0.5 Gram(s)1%
Fennel oil10 mg--
Castor Oil650 mg--

Other ingredients: Softgel Capsule

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

Suggested Usage: Take 1 softgel 1 to 2 times daily with food as needed.

General Statements

Castor Oil is an oil derived from the beans of the castor plant (Ricinus communis). Castor Oil has long been recognized as a powerful laxative that may be used for the relief of occasional constipation.*

Natural color variation may occur in product.

Natural laxative* ~ Supports digestive regularity*

Nutritional Oils Family owned since 1968.

Please recycle.

FDA Disclaimer Statement

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease.

Precautions

Caution: For adults only. Castor oil is a laxative.

This product is not intended for pregnant or nursing women. Consult physician if taking medication or have a medical condition (including any gastric or intestinal disorders).

Do not exceed recommended dose. This product is not intended for long term use. Discontinue use if gastric upset or diarrhea occurs.

Keep out of reach of children.

Not manufactured with yeast, wheat, gluten, soy, corn, milk, egg, fish or shellfish ingredients. Produced in a GMP facility that processes other ingredients containing these allergens.

General

CODE 1723 V5

Formula

~ With fennel oil

Seals/Symbols

Non-GMO

GMP Quality Assured

Formulation

Non-GMO

Not manufactured with yeast, wheat, gluten, soy, corn, milk, egg, fish or shellfish ingredients.

FDA Statement of Identity

A Dietary Supplement

Storage

Store in a cool, dry place after opening.

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

See for yourself

Castor Oil 650 mg by NOW label

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

Castor Oil 650 mg 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 Castor Oil 650 mg by NOW

These are the 2 active ingredients this product is made of. Select any to open its full monograph.

Serving size1 Softgel(s) Dosage formSoftgel Capsule 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.

Fennel oil

Interacts with
740 drugs
10 mg per serving

Fennel is a Mediterranean herb widely used as a food and spice, and traditionally taken for digestive complaints, colic, and menstrual cramps. Some sm...

Fennel oil monograph & interactions

Castor Oil

650 mg per serving

Other (inactive) ingredients: Softgel Capsule. These complete the product’s ingredient list but are not active constituents.

Interaction report

Castor Oil 650 mg by NOW Drug Interactions

Want to check YOUR meds against Castor Oil 650 mg?

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
740Drugs
740 Moderate

Ingredients driving the most interactions

Fennel oil 740

Individual Drug Interactions

The ingredients in Castor Oil 650 mg interact with 740 drugs. Click any drug to see the details.

1 of the 2 ingredients in Castor Oil 650 mg interact with drugs. Each result below shows which ingredient is responsible. Fennel oil

Each ingredient & the kinds of drugs it affects

For each ingredient in Castor Oil 650 mg with known interactions, here are the types of medications it can affect. Open any type for the detail — or search your exact drug in the checker above.

Fennel oil6 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 oil full monograph & interactions
The maker

Brand information

Manufacturer and brand details for Castor Oil 650 mg, from the product label.

NOW

See all NOW products
Name
NOW FOODS
Street Address
395 S. Glen Ellyn Rd.
City
Bloomingdale
State
IL
ZipCode
60108
Web Address
www.nowfoods.com
Pharmacist Counseling Corner

Castor Oil 650 mg by NOW: Common Questions

Does Castor Oil 650 mg by NOW interact with any medications?
Yes. Based on its ingredients, Castor Oil 650 mg has a known interaction with 740 medications. Use the checker to see how it interacts with a specific drug.
How can one product interact with so many drugs?
Castor Oil 650 mg contains 2 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 while I'm pregnant?
The safety data advises against medicinal or concentrated amounts of fennel oil during pregnancy due to limited safety data and possible hormone-like effects. Talk with your doctor or pharmacist before taking this product if you're pregnant or planning to become pregnant.
Is fennel oil safe while breastfeeding?
Food amounts of fennel are likely fine, but medicinal doses like those in this supplement aren't well studied while breastfeeding. Ask your pharmacist or doctor whether this product is right for you if you're nursing.
What does fennel oil actually do in this product?
Fennel oil is possibly effective for painful periods (dysmenorrhea). For anxiety, bronchitis, bedwetting, and cholera, we don't have reliable evidence yet.
What side effects might I experience?
Most people tolerate fennel oil well. Some report stomach discomfort, sensitivity to sun exposure, or allergic reactions like sneezing, coughing, or itchy mouth. Rarely, breathing difficulty or wheezing can occur; if that happens, stop and seek help.
Does this interact with my blood pressure medication?
We have no documented interactions between fennel oil and blood pressure drugs in our data. Still, run your exact medication through the checker on this page to be sure.
What's actually in this capsule besides the oil?
The active ingredients are fennel oil and castor oil. The capsule itself is a softgel — the inactive ingredient. We have no interaction or safety data on castor oil, so we can't speak to its effects.

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

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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.

Castor Oil 650 mg label
Go deeper

The Full Monographs Behind Castor Oil 650 mg’s Ingredients

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

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 →
Sources

Sources & How We Checked

Castor Oil 650 mg'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 17 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.

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 →

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

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