Drug & supplement interaction

Soy + Finasteride

Finasteride brand names: Propecia, Proscar.

No Known Interaction

Medically reviewed by Dr. Brian Staiger, PharmD, BCPS · Updated July 2026 · Pair last verified Sep 13, 2026

The bottom line No known interaction

We found no known interaction between Soy and Finasteride in our sources. Absence of a documented interaction is not the same as proven safety, and does not guarantee one does not exist. Do not start, stop, or change a medication or supplement based on this page; confirm with your pharmacist or doctor first. Additionally, although there is no interaction, the two are separately associated with some of the same side effects, which would make a new symptom harder to attribute to one or the other.

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Interaction report

Soy and Finasteride

We checked these two against our interaction database. Here is what we found.

No Known Interaction Found

We did not find a documented interaction between Finasteride and Soy in our sources. This does not guarantee that the combination is completely free of risk — there is often limited research on supplements and herbal products, especially around drug interactions.

If you decide to take both, the practical routine is simple: add one new thing at a time and note the date you started it. If the combination is going to disagree with you, it usually shows in the first days to a couple of weeks — and a start date turns “I’ve been feeling off” into something a pharmacist can actually work with. Do not stop a prescribed medicine on your own.

Always talk with your pharmacist or doctor before making changes to your medications or supplements, particularly if you take several medications or have an ongoing health condition.

Soy safety at a glance

Soy overall Use caution Soy foods are generally safe for most people, but concentrated isoflavone supplements deserve more caution.

Pregnancy Likely Safe When used orally in amounts commonly found in foods. Read the full pregnancy detail

Breastfeeding Likely Safe When used orally in amounts commonly found in foods. A single 20-gram dose of roasted soybeans, containing 37 mg isoflavones, produces four to six times less is... Read the full breastfeeding detail

Pregnancy & breastfeeding ratings are from Natural Medicines (Therapeutic Research Center) — the full detail is in the Special populations card below. Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

Still wondering about combining Finasteride and Soy? Ask Dr. Brian Staiger, PharmD, BCPS directly ›

How we checked

Why No Interaction Is Listed for Finasteride

Interactions in our licensed database are recorded against drug classes, not just single drug names. Finasteride is filed under 3 classifications — including cytochrome p450 3a4 (cyp3a4) substrates, oral drugs. Soy has documented interactions with 12 drug classes — the most serious being monoamine oxidase inhibitors (maois) (major), antidiabetes drugs (moderate) and antihypertensive drugs (moderate) — and none of Finasteride’s classifications are among them.

Classification data comes from our licensed Natural Medicines dataset. A medication can belong to classes beyond those recorded there, so this describes how the check was run — it is not a safety guarantee.

Keep it in perspective

Soy Does Interact With Other Medications

Soy has 9 major, 343 moderate, 259 minor known drug interactions in our database — Finasteride isn’t one of them. If you take anything else, check it against the full list below.

Major 9 Moderate 343 Minor 259 No known interaction 2,219 (incl. Finasteride)

Taking anything else?

Check Another of Your Medications Against Soy

Covers the 2,830 medications we’ve checked against Soy. Pick one to open its full report.

What to actually watch for

No Interaction Found — But Data Suggests Soy and Finasteride May Share Several of the Same Side Effects

This is not an interaction. Neither one changes how your body handles the other, and nothing here says they react together. What our sources do show is that each has separately been linked to the effects below — so taking both can make those effects more likely to turn up, and harder to pin on one or the other if they do. 2 of them are worth acting on rather than waiting out — marked below.

A severe allergic reaction Worth acting on Additional detail
Soy
“Orally, soy can cause allergic reactions such as skin rash and itching in some people. In an 11-year-old female, allergy to soy protein resulting in a delayed itching papular rash was thought to be responsible for the reaction to injected benzathine benzylpenicillin containing possible soy protein-contaminated soy lecithin.

Topically, soy-based ingredients were responsible for the development of hand atopic dermatiti…”

Soy · Natural Medicines adverse-effect record, reported in allergic rhinitis (hay fever).
3 sources cited

6412. Teixeira SR, Potter SM, Weigel R, et al. Effects of feeding 4 levels of soy protein for 3 and 6 wk on blood lipids and apolipoproteins in moderately hypercholesterolemic men. Am J Clin Nutr 2000;71:1077-84. PubMed

96422. Barni S, Mori F, Pantano S, Novembre E. Adverse reaction to benzathine benzylpenicillin due to soy allergy: a case report. J Med Case Rep. 2015;9:134. PubMed

96000. Yagami A, Suzuki K, Nakamura M, et al. Case of anaphylactic reaction to soy following percutaneous sensitization by soy-based ingredients in cosmetic products. J Dermatol. 2015;42(9):917-8. PubMed
Finasteride

Listed in the ADVERSE REACTIONS section of the FDA label for Finasteride. Read the label on DailyMed ›
An allergic reaction Worth acting on Additional detail

Soy

“Orally, soy is well tolerated.

Most Common Adverse Effects:

Orally: Bloating, constipation, diarrhea, and nausea.

All ROAs: Allergic reactions.”

Soy · Natural Medicines adverse-effect record, reported in constipation.

Finasteride

Listed in the ADVERSE REACTIONS section of the FDA label for Finasteride. Read the label on DailyMed ›
A stuffy or runny nose Additional detail
Soy
“Inhaled soy dust and soy hull aeroallergen can trigger symptoms of asthma and allergic rhinitis.”

Soy · Natural Medicines adverse-effect record, reported in allergic rhinitis (hay fever).
3 sources cited

5084. Codina R, Ardusso L, Lockey RF, et al. Sensitization to soybean hull allergens in subjects exposed to different levels of soybean dust inhalation in Argentina. J Allergy Clin Immunol 2000;105:570-6. PubMed

5085. Anto JM, Sunyer J, Rodriguez-Roisin R, et al. Community outbreaks of asthma associated with inhalation of soybean dust. Toxicoepidemiological Committee. N Engl J Med 1989;320:1097-1102. PubMed

5086. White MC, Etzel RA, Olson DR, Goldstein IF. Re-examination of epidemic asthma in New Orleans, Louisianna, in relation to the presence of soy at the harbor. Am J Epidemiol 1997;145:432-8.
Finasteride

Listed in the ADVERSE REACTIONS section of the FDA label for Finasteride. Read the label on DailyMed ›
Itching / A skin rash Additional detail

Soy

Recorded for Soy in the same Natural Medicines adverse-effect record shown under A severe allergic reaction above.

Finasteride

Listed in the ADVERSE REACTIONS section of the FDA label for Finasteride. Read the label on DailyMed ›
Tiredness Additional detail
Soy
“In the 1950s and 1960s, cases of altered thyroid function, particularly goiter, were reported in children taking soy formula. However, adding iodine to soy formula or replacing soy flour in formula with soy protein isolate has nearly eliminated the risk of altered thyroid function in most infants.

In adults, there is some evidence that soy intake can alter thyroid function.”

Soy · Natural Medicines adverse-effect record, reported in constipation.
6 sources cited

75353. Rozman, K. K., Bhatia, J., Calafat, A. M., Chambers, C., Culty, M., Etzel, R. A., Flaws, J. A., Hansen, D. K., Hoyer, P. B., Jeffery, E. H., Kesner, J. S., Marty, S., Thomas, J. A., and Umbach, D. NTP-CERHR expert panel report on the reproductive and dev

75651. Van Wyk JJ, Arnold MB, Wynn J, and et al. The effects of a soybean product on thyroid function in humans. Pediatrics 1959;24:752-760. DOI

75206. Fitzpatrick, M. Soy formulas and the effects of isoflavones on the thyroid. N.Z.Med J 2-11-2000;113(1103):24-26.

7806. Persky VW, Turyk ME, Wang L, et al. Effect of soy protein on endogenous hormones in postmenopausal women. Am J Clin Nutr 2002;75:145-53. PubMed

6466. Divi RL, Chang HC, Doerge DR. Anti-thyroid isoflavones from soybean: isolation, characterization, and mechanisms of action. Biochem Pharmacol 1997;54:1087-96. PubMed

75311. Messina, M. and Redmond, G. Effects of soy protein and soybean isoflavones on thyroid function in healthy adults and hypothyroid patients: a review of the relevant literature. Thyroid 2006;16(3):249-258. PubMed
Finasteride

Listed in the ADVERSE REACTIONS section of the FDA label for Finasteride. Read the label on DailyMed ›

Reported for Soy but not commonly for Finasteride: stomach upset, a change in thyroid levels, memory problems and constipation.

Effects for Finasteride come from the ADVERSE REACTIONS section of its FDA label; effects for Soy come from the Natural Medicines adverse-effect record, quoted above. Wording is matched across sources by our own clinical vocabulary, so treat this as a prompt to pay attention, not a diagnosis.

Special populations

Soy in Pregnancy & Breastfeeding

Pregnancy Likely Safe

When used orally in amounts commonly found in foods.

Pregnancy Possibly Unsafe

When used orally in medicinal amounts. Soy contains mildly estrogenic constituents. Theoretically, therapeutic use of soy might adversely affect fetal development; avoid using.

Lactation Likely Safe

When used orally in amounts commonly found in foods. A single 20-gram dose of roasted soybeans, containing 37 mg isoflavones, produces four to six times less isoflavones in breast milk than provided in a soy-based infant formula. There is insufficient reliable information available about the safety of long-term use of therapeutic amounts of soy during lactation.

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

Overlapping uses

What Finasteride Is Prescribed For, and What Soy Has Been Studied For

These two come up together because they touch the same health topic — not because they do the same job. Finasteride is a prescription medicine with approved uses on its FDA label. Soy is a supplement: what follows is what researchers have looked at it for, and how strong that evidence is.

Finasteride is prescribed for: Finasteride tablets (including the brand Proscar) are used in men with an enlarged prostate (benign prostatic hyperplasia, or BPH) to improve urinary symptoms, lower the risk of acute urinary retention (a sudden inability to urinate), and reduce the need for prostate surgery. Finasteride tablets may also be used alongside the alpha-blocker doxazosin to slow the progression of BPH symptoms. Propecia (and finasteride 1 mg coated tablets) is indicated for the treatment of male pattern hair loss (androgenetic alopecia) in men only. Propecia is not approved for use in women, and its effectiveness for hair loss at the temples has not been established.

Read the rest of what Finasteride is prescribed for

Finasteride is not approved for the prevention of prostate cancer.

Soy has been studied for:

Prostate cancer studied, not established Soy has been studied for this. Natural Medicines rates the evidence: Insufficient Reliable Evidence To Rate Read what the research shows

Soy for prostate cancer

It is unclear if oral soy is beneficial for the treatment or prevention of prostate cancer; research is conflicting.

Effectiveness ratings and the research summaries above are the verbatim record from the Natural Medicines database, which grades evidence from “Effective” down to “Insufficient Reliable Evidence To Rate”. A rating below the top of that scale means researchers have looked at it — not that it works, and never that it can stand in for a prescribed medicine. Do not stop or replace Finasteride on your own; if you are taking Soy for the same health topic, tell your prescriber, especially if the medicine is being adjusted to a target.

From our Q&A

Questions About Soy or Finasteride

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Soy or Finasteride, not necessarily both, but if one is close to what you were about to ask it will usually go further than a database entry can:

Not quite your question? Ask our pharmacists directly — it is free, there is no account required, and answers usually come back within 24 hours.

Everything else you take

See Every Supplement That Interacts With Finasteride

This page covers Soy only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Finasteride page lists 138 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Grapefruit (major), St. John's Wort (major), Acacia Rigidula (moderate) and Adrafinil (moderate).

By severity: 3 major · 94 moderate · 41 minor.

From our pharmacist’s overview on the Finasteride page

“The supplement list for finasteride (Propecia, Proscar) is one I would read carefully rather than skim, because three of its 138 entries are rated major. Almost everything here works through the same liver enzyme, CYP3A4, that clears finasteride.”

Reviewed by 2 · Jul 18, 2026

Open the Finasteride interaction page

One more smart check

Taking Soy as Part of a Dietary Supplement Product? Check It for Interactions

We hold 821 real supplement products containing Soy, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Soy. Even though Soy itself has no known interaction with Finasteride, another ingredient on your label might. Find your product and we’ll check every ingredient on its label:

How much people look this up

Where Soy and Finasteride Sit Against Everything Else

Out of every supplement and medication people look up on HelloPharmacist, here is where these two land this week — and which way each has been moving.

Supplement Soy

Top 25%

#224 of 1,452 supplements looked up here in the last 7 days

29 days ago today

Medication Finasteride

Top 5%

#63 of 2,830 medications looked up here in the last 7 days

29 days ago today

Position among everything looked up on this site, not a measure of how commonly either one is used or how important it is. A supplement can climb this list because of a news story. It counts every request to the page, automated ones included, and nothing here identifies anyone.

Where does our data come from?

Source: the Natural Medicines (TRC Healthcare) clinical database — the evidence-graded professional reference for herb & supplement interactions.
Citation library: 103,510 references behind our interaction content, 65,311 of them resolved to verified PubMed/DOI sources. See every Soy reference on this page ↓
Freshness: we automatically re-check this combination every week — this pair was last verified September 13, 2026. The Soy and Finasteride records this page draws on were last updated July 11, 2026.
What “no known interaction” means: no documented interaction in the sources above — not a guarantee of safety. Supplements are studied far less than prescription drugs, so we say exactly what the evidence supports, and nothing more.

Data structure & sourcing designed and verified by Dr. Brian Staiger, PharmD, BCPS.

Supplement

About Soy

What is Soy?

Menopause symptoms (hot flashes)
Heart and cholesterol health
Bone health
Plant-based protein source
General nutrition

Soy is a nutritious bean that is a staple food and a popular source of plant protein and isoflavones. Eating soy foods as part of a balanced diet is generally considered safe for most people, and there is moderate evidence it may modestly help cholesterol and some menopause symptoms, though results vary. Talk with your pharmacist or doctor before using concentrated soy isoflavone supplements, especially if you have a history of hormone-sensitive conditions.

Glycine max · Fabaceae · Bean (seed) · Whole soybeans, soy milk, tofu, tempeh, edamame, soy protein powder, isoflavone capsules, soy lecithin

An interaction check asks whether these two react with each other — it does not ask whether Soy is a good idea for someone in your situation. Here is what our Soy record says about it on its own.

Soy: dosing

There is no single official dose of soy for any health condition. Amounts used in studies vary widely, and a standardized supplement dose has not been firmly established.As a food, soy is simply part of a normal diet. For supplements such as isoflavone capsules or soy protein powder, follow the directions on the product label.

From our Soy monograph — the full record covers uses, side effects and every documented interaction.

Read the full Soy monograph & all interactions

Medication

About Finasteride

What Is Finasteride Used For?

Brand names: Propecia, Proscar

Finasteride tablets (including the brand Proscar) are used in men with an enlarged prostate (benign prostatic hyperplasia, or BPH) to improve urinary symptoms, lower the risk of acute urinary retention (a sudden inability to urinate), and reduce the need for prostate surgery. Finasteride tablets may also be used alongside the alpha-blocker doxazosin to slow the progression of BPH symptoms.

Propecia (and finasteride 1 mg coated tablets) is indicated for the treatment of male pattern hair loss (androgenetic alopecia) in men only. Propecia is not approved for use in women, and its effectiveness for hair loss at the temples has not been established. Finasteride is not approved for the prevention of prostate cancer.

See full Finasteride drug information

Keep checking

Other Drugs & Soy

Browse every other medication we’ve checked against Soy — both the ones with a known interaction and the ones without. Select any drug for the full detail.

9Major

343Moderate

259Minor

2,218No known interaction

9 Major 343 Moderate 259 Minor 2,218 No interaction

Major

9 interactions

Moderate

343 interactions

Showing 60 of 343 moderate interactions — see all 343 on the Soy page.

Minor

259 interactions

Showing 60 of 259 minor interactions — see all 259 on the Soy page.

No interaction 2,218 drugs checked — show the list

We also checked Soy against these medications and found no known interaction in our sources. Open any page to confirm.

Showing the 60 most looked-up of 2,218 medications checked with no known interaction — see the full Soy list.

See the full Soy interactions page

See every supplement checked against Finasteride, ranked by severity

Evidence & sources

Soy References

The 88 references that drive our Soy 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.

Franke AA, Custer LJ, Tanaka Y. Isoflavones in human breast milk and other biological fluids. Am J Clin Nutr 1998;68:1466-73. PubMed
Albertazzi P, Pansini F, Bonaccorsi G, et al. The effect of dietary soy supplementation on hot flushes. Obstet Gynecol 1998;91:6-11. PubMed
Lu LJ, Anderson KE, Grady JJ, et al. Decreased ovarian hormones during a soya diet: implications for breast cancer prevention. Cancer Res 2000;60:4112-21.
Pino AM, Valladares LE, Palma MA, et al. Dietary isoflavones affect sex hormone-binding globulin levels in postmenopausal women. J Clin Endocrinol Metab 2000;85:2797-800. DOI
Nisley N, Klepser T. Phytoestrogens for the prevention and treatment of osteoporosis. Alt Med Alert 1999 Dec;138-42.
McMichael-Phillips DF, Harding C, Morton M, et al. Effects of soy-protein supplementation on epithelial proliferation in the histologically normal human breast. Am J Clin Nutr 1998;68:1431S-5S. PubMed
Petrakis NL, Barnes S, King EB, et al. Stimulatory influence of soy protein isolate on breast secretion in pre- and postmenopausal women. Cancer Epidemiol Biomarkers Prev 1996;5:785-94.
Baird DD, Umbach DM, Lansdell L, et al. Dietary intervention study to assess estrogenicity of dietary soy among postmenopausal women. J Clin Endocrinol Metab 1995;80:1685-90. DOI
Duncan AM, Underhill KE, Xu X, et al. Modest hormonal effects of soy isoflavones in postmenopausal women. J Clin Endocrinol Metab 1999;84:3479-84. PubMed
Ginsburg J, Prelevic GM. Lack of significant hormonal effects and controlled trials of phyto-oestrogens. Lancet 2000;355:163-4. PubMed
Anthony MS. Soy and cardiovascular disease: Cholesterol lowering and beyond. J Nutr 2000;130:662S-3S. PubMed
Hargreaves DF, Potten CS, Harding C, et al. Two-week dietary soy supplementation has an estrogenic effect on normal premenopausal breast. J Clin Endocrinol Metab 1999;84:4017-24. DOI
Lamartiniere CA. Protection against breast cancer with genistein: a component of soy. Am J Clin Nutr 2000;71:1705S-7S. PubMed
Electronic Code of Federal Regulations. Title 21. Part 182 -- Substances Generally Recognized As Safe. Available at: https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?CFRPart=182
Codina R, Ardusso L, Lockey RF, et al. Sensitization to soybean hull allergens in subjects exposed to different levels of soybean dust inhalation in Argentina. J Allergy Clin Immunol 2000;105:570-6. PubMed
Anto JM, Sunyer J, Rodriguez-Roisin R, et al. Community outbreaks of asthma associated with inhalation of soybean dust. Toxicoepidemiological Committee. N Engl J Med 1989;320:1097-1102. PubMed
White MC, Etzel RA, Olson DR, Goldstein IF. Re-examination of epidemic asthma in New Orleans, Louisianna, in relation to the presence of soy at the harbor. Am J Epidemiol 1997;145:432-8.
Murkies A, Dalais FS, Briganti EM, et al. Phytoestrogens and breast cancer in postmenopausal women: a case control study. Menopause 2000;7:289-96. PubMed
Setchell KD, Cassidy A. Dietary isoflavones: biological effects and relevance to human health. J Nutr 1999;129:758S-67S. PubMed
Teixeira SR, Potter SM, Weigel R, et al. Effects of feeding 4 levels of soy protein for 3 and 6 wk on blood lipids and apolipoproteins in moderately hypercholesterolemic men. Am J Clin Nutr 2000;71:1077-84. PubMed
White LR, Petrovitch H, Ross GW, et al. Brain aging and midlife tofu consumption. J Am Coll Nutr 2000;19:242-55. PubMed
Grodstein F, Mayeux R, Stampfer MJ. Tofu and cognitive function: food for thought. J Am Coll Nutr 2000;19:207-9. PubMed
Divi RL, Chang HC, Doerge DR. Anti-thyroid isoflavones from soybean: isolation, characterization, and mechanisms of action. Biochem Pharmacol 1997;54:1087-96. PubMed
de Lemos ML. Effects of soy phytoestrogens genistein and daidzein on breast cancer growth. Ann Pharmacother 2001;35:1118-21. PubMed
Strom BL, Schinnar R, Ziegler EE, et al. Exposure to soy-based formula in infancy and endocrinological and reproductive outcomes in young adulthood. JAMA 2001;286:807-14. PubMed
Goodman MT, Wilkens LR, Hankin JH, et al. Association of soy and fiber consumption with the risk of endometrial cancer. Am J Epidemiol 1997;146:294-306. PubMed
Wu AH, Yang D, Pike MC. A meta-analysis of soyfoods and risk of stomach cancer: the problem of potential confounders. Cancer Epidemiol Biomarkers Prev 2000;9:1051-8.
Ji BT, Chow WH, Yang G, et al. Correspondence re: AH Wu et al, A meta-analysis of soyfoods and risk of stomach cancer: the problem of potential confounders. Cancer Epidemiol Biomarkers Prev 2001;10:570.
Foth D, Cline JM. Effects of mammalian and plant estrogens on mammary glands and uteri of macaques. Am J Clin Nutr 1998;68:1413S-7S. PubMed
Duncan AM, Merz BE, Xu X, et al. Soy isoflavones exert modest hormonal effects in premenopausal women. J Clin Endocrinol Metab 1999;84:192-7. DOI
Morito K, Hirose T, Kinjo J, et al. Interaction of phytoestrogens with estrogen receptors alpha and beta. Biol Pharm Bull 2001;24:351-6. PubMed
Persky VW, Turyk ME, Wang L, et al. Effect of soy protein on endogenous hormones in postmenopausal women. Am J Clin Nutr 2002;75:145-53. PubMed
Ju YH, Doerge DR, Allred KF, et al. Dietary Genistein Negates the Inhibitory Effect of Tamoxifen on Growth of Estrogen-dependent Human Breast Cancer (MCF-7) Cells Implanted in Athymic Mice. Cancer Res 2002;62:2474-7 .
Cambria-Kiely JA. Effect of soy milk on warfarin efficacy. Ann Pharmacother 2002;36:1893-6.. PubMed
Ziegler RG, Hoover RN, Pike MC, et al. Migration patterns and breast cancer risk in Asian-American women. J Natl Cancer Inst 1993;85:1819-27.. PubMed
Brown BD, Thomas W, Hutchins A, et al. Types of dietary fat and soy minimally affect hormones and biomarkers associated with breast cancer risk in premenopausal women. Nutr Cancer 2002;43:22-30.. PubMed
Sun CL, Yuan JM, Arakawa K, et al. Dietary soy and increased risk of bladder cancer: the Singapore Chinese Health Study. Cancer Epidemiol Biomarkers Prev 2002;11:1674-7.
Balk JL, Whiteside DA, Naus G, et al. A pilot study of the effects of phytoestrogen supplementation on postmenopausal endometrium. J Soc Gynecol Investig 2002;9:238-42.. DOI
Horn-Ross PL, John EM, Canchola AJ, et al. Phytoestrogen intake and endometrial cancer risk. J Natl Cancer Inst 2003;95:1158-64.. PubMed
Kumar NB, Cantor A, Allen K et al. The specific role of isoflavones in reducing prostate cancer risk. Prostate 2004;59:141-7. PubMed
Chen A, Rogan WJ. Isoflavones in soy infant formula: a review of evidence for endocrine and other activity in infants. Annu Rev Nutr 2004;24:33-54. PubMed
Chen YM, Ho SC, Lam SS, et al. Soy isoflavones have a favorable effect on bone loss in Chinese postmenopausal women with lower bone mass: a double-blind, randomized, controlled trial. J Clin Endocrinol Metab 2003;88:4740-7. PubMed
Unfer V, Casini ML, Costabile L, et al. Endometrial effects of long-term treatment with phytoestrogens: a randomized, double-blind, placebo-controlled study. Fertil Steril 2004;82:145-8. PubMed
Bruce B, Messina M, Spiller G. Isoflavone supplements do not affect thyroid function in iodine-replete postmemopausal women. J Med Food 2003;6:309-16.
He J, Gu D, Wu X, et al. Effect of soybean protein on blood pressure: A randomized, controlled trial. Ann Intern Med 2005;143:1-9. PubMed
Kaari C, Haidar MA, Junior JMS, et al. Randomized clinical trial comparing conjugated equine estrogens and isoflavones in postmenopausal women: a pilot study. Maturitas 2006;53:49-58. PubMed
Sacks FM, Lichtenstein A, Van Horn L, et al. Soy protein, isoflavones, and cardiovascular health. An American Heart Association Science Advisory for Professionals from the Nutrition Committee. Circulation 2006;113:1034-44. PubMed
Jones JL, Daley BJ, Enderson BL, et al. Genistein inhibits tamoxifen effects on cell proliferation and cell cycle arrest in T47D breast cancer cells. Am Surg 2002;68:575-7. DOI
Shulman KI, Walker SE. Refining the MAOI diet: tyramine content of pizzas and soy products. J Clin Psychiatry 1999;60:191-3. DOI
Gardner DM, Shulman KI, Walker SE, Tailor SA. The making of a user friendly MAOI diet. J Clin Psychiatry 1996;57:99-104.
Walker SE, Shulman KI, Tailor SA, Gardner D. Tyramine content of previously restricted foods in monoamine oxidase inhibitor diets. J Clin Psychopharmacol 1996;16:383-8. PubMed
Krebs EE, Ensrud KE, MacDonald R, Wilt TJ. Phytoestrogens for treatment of menopausal symptoms: a systematic review. Obstet Gynecol 2004;104:824-36. PubMed
Wang G, Xiao CQ, Li Z, et al. Effect of soy extract administration on losartan pharmacokinetics in healthy female volunteers. Ann Pharmacother 2009;43:1045-9. PubMed
Jabbar MA, Larrea J, Shaw RA. Abnormal thyroid function tests in infants with congenital hypothyroidism: the influence of soy-based formula. J Am Coll Nutr. 1997;16(3):280-2. PubMed
Conrad SC, Chiu H, Silverman BL. Soy formula complicates management of congenital hypothyroidism. Arch Dis Child. 2004;89(1):37-40. PubMed
Chen, Y., Xiao, C. Q., He, Y. J., Chen, B. L., Wang, G., Zhou, G., Zhang, W., Tan, Z. R., Cao, S., Wang, L. P., and Zhou, H. H. Genistein alters caffeine exposure in healthy female volunteers. Eur.J Clin.Pharmacol. 2011;67(4):347-353. PubMed
Whelan, A. M., Jurgens, T. M., and Naylor, H. Herbs, vitamins and minerals in the treatment of premenstrual syndrome: a systematic review. Can.J.Clin.Pharmacol. 2009;16(3):e407-e429.
Lydeking-Olsen, E., Beck-Jensen, J. E., Setchell, K. D., and Holm-Jensen, T. Soymilk or progesterone for prevention of bone loss--a 2 year randomized, placebo-controlled trial. Eur.J Nutr. 2004;43(4):246-257. PubMed
Hill, D. J., Heine, R. G., Cameron, D. J., Francis, D. E., and Bines, J. E. The natural history of intolerance to soy and extensively hydrolyzed formula in infants with multiple food protein intolerance. J.Pediatr. 1999;135(1):118-121. PubMed
Fitzpatrick, M. Soy formulas and the effects of isoflavones on the thyroid. N.Z.Med J 2-11-2000;113(1103):24-26.
Li, Z., Hong, K., Saltsman, P., DeShields, S., Bellman, M., Thames, G., Liu, Y., Wang, H. J., Elashoff, R., and Heber, D. Long-term efficacy of soy-based meal replacements vs an individualized diet plan in obese type II DM patients: relative effects on w
Post-Skagegard, M., Vessby, B., and Karlstrom, B. Glucose and insulin responses in healthy women after intake of composite meals containing cod-, milk-, and soy protein. Eur J Clin Nutr 2006;60(8):949-954. PubMed
Mclachlan, J. A., Simpson, E., and Martin, M. Endocrine disrupters and female reproductive health. Best.Pract Res Clin Endocrinol.Metab 2006;20(1):63-75. PubMed
Messina, M. and Redmond, G. Effects of soy protein and soybean isoflavones on thyroid function in healthy adults and hypothyroid patients: a review of the relevant literature. Thyroid 2006;16(3):249-258. PubMed
Rozman, K. K., Bhatia, J., Calafat, A. M., Chambers, C., Culty, M., Etzel, R. A., Flaws, J. A., Hansen, D. K., Hoyer, P. B., Jeffery, E. H., Kesner, J. S., Marty, S., Thomas, J. A., and Umbach, D. NTP-CERHR expert panel report on the reproductive and dev
Azadbakht, L., Kimiagar, M., Mehrabi, Y., Esmaillzadeh, A., Padyab, M., Hu, F. B., and Willett, W. C. Soy inclusion in the diet improves features of the metabolic syndrome: a randomized crossover study in postmenopausal women. Am J Clin Nutr 2007;85(3):7 PubMed
Berseth, C. L., Johnston, W. H., Stolz, S. I., Harris, C. L., and Mitmesser, S. H. Clinical response to 2 commonly used switch formulas occurs within 1 day. Clin.Pediatr.(Phila) 2009;48(1):58-65. PubMed
Altorf-van der Kuil, W., Engberink, M. F., Brink, E. J., van Baak, M. A., Bakker, S. J., Navis, G., van, 't, V, and Geleijnse, J. M. Dietary protein and blood pressure: a systematic review. PLoS.One. 2010;5(8):e12102. PubMed
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Liu, Z. M., Chen, Y. M., and Ho, S. C. Effects of soy intake on glycemic control: a meta-analysis of randomized controlled trials. Am.J.Clin.Nutr. 2011;93(5):1092-1101. PubMed
Iyngkaran, N., Yadav, M., Looi, L. M., Boey, C. G., Lam, K. L., Balabaskaran, S., and Puthucheary, S. D. Effect of soy protein on the small bowel mucosa of young infants recovering from acute gastroenteritis. J Pediatr.Gastroenterol.Nutr 1988;7(1):68-75. DOI
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Medication overviews come from MedlinePlus (NIH); supplement label data from the NIH Dietary Supplement Label Database. Content is written and reviewed by licensed HelloPharmacist pharmacists — see our data sources and editorial standards.

Pharmacist Counseling Corner

Taking Soy and Finasteride Together: Common Questions

Is it safe to take Soy with Finasteride?

We do not list a known interaction between Soy and Finasteride. That does not guarantee the combination is risk-free, so confirm with your pharmacist or doctor — especially if you take other medications or have a health condition.

Do Soy and Finasteride have any of the same side effects?

Yes — our sources link each of them separately to 6 of the same effects. That is not an interaction: neither changes how your body handles the other. It does mean that if one of those effects turns up, it can be harder to tell which one is behind it. They are listed on this page with the source behind each.

Are Soy and Finasteride used for the same thing?

They overlap in purpose, which usually means the real question is whether you need both rather than whether they are safe together. This page lists the shared uses and how strong the evidence is for Soy in each. That is a conversation for your prescriber, especially if Finasteride is being adjusted to a target.

How was the Soy and Finasteride combination checked?

Interactions in our licensed database are recorded against drug classes. Finasteride is filed under 3 classifications, and Soy has documented interactions with 12 drug classes — none of Finasteride's classifications are among them. A medication can belong to classes beyond those recorded in our dataset, so this describes how the check was run rather than guaranteeing safety.

Does Soy interact with any other medications?

Yes. Soy has 611 documented drug interactions in our database — Finasteride is simply not one of them. If you take anything else, it is worth checking each one; they are all listed on this page.

Does Finasteride interact with any supplements?

Yes. Finasteride has documented interactions with 138 supplements in our database — Soy is not one of them. The Finasteride interaction page linked on this page lists every one, ranked by severity.

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

Where next

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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.