Herb & supplement monograph

Soy Drug Interactions, Uses, Effectiveness, Safety & More

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

What is this page for?

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

But these pages have grown well beyond that into a full monograph — what Soy 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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Soy Drug Interactions: The Bottom Line

From the HelloPharmacist Editorial Team · Updated July 2026

Based on the available evidence, the overall risk of a clinically significant Soy drug interaction appears low for most people. Only a small handful of the listed interactions are rated major, and most of the moderate ones rest on theoretical or limited human evidence.

Interactions deserving the most attention

The clearest concern is with MAOIs, a class of antidepressants: fermented soy foods like tofu and soy sauce contain tyramine, which these drugs stop the body from breaking down, raising the risk of a dangerous blood pressure spike. Soy may also reduce absorption of levothyroxine, an effect seen in infants given soy formula, and it can lower blood sugar, which could add to the effect of diabetes medications. There is also a single report of soy milk weakening warfarin's blood-thinning effect, so people on warfarin should watch for changes.

What the rest of the list means

Soy appears alongside hundreds of medications, but a long list does not mean every combination is harmful. Most entries come from lab or animal research or from possible effects on enzymes the body uses to clear medications. In fact, when one of these predicted enzyme effects was tested in people, medication levels did not change in a meaningful way.

Check your medications against Soy

Based on HelloPharmacist’s Soy interaction data and reviewed under our editorial standards.

Interaction report

Drugs that interact with Soy

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

9 major interactions. These combinations can be clinically significant — best avoided, or used only with close professional supervision. Always check with your pharmacist before combining them with Soy.

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

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

AI summaries are generated from our Soy 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 Soy 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 Soy affects

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

All 12 drug categories Soy interacts with

Monoamine Oxidase Inhibitors (maois)Antidiabetes DrugsAntihypertensive DrugsCaffeineDiuretic DrugsEstrogensLevothyroxine (synthroid, Others)ProgesteroneTamoxifen (nolvadex)Warfarin (coumadin)Antibiotic DrugsCytochrome P450 2c9 (cyp2c9) Substrates

Monoamine Oxidase Inhibitors (Maois)

Taking soy products containing high amounts of tyramine along with MAOIs can increase the risk of hypertensive crisis.
Fermented soy products such as tofu and soy sauce contain tyramine, a naturally occurring chemical that affects blood pressure regulation. The metabolism of tyramine is decreased by MAOIs. Consuming more than 6 mg of tyramine while taking an MAOI can increase the risk of hypertensive crisis. The amount of tyramine in fermented soy products is usually less than 0.6 mg per serving; however, there can be significant variation depending on the specific product used, storage conditions, and length of storage. Storing one brand of tofu for a week can increase tyramine content from 0.23 mg to 4.8 mg per serving. Advise patients taking MAOIs to avoid fermented soy products that contain high amounts of tyramine.

Likelihood Likely Evidence C

Antidiabetes Drugs

Soy can lower blood glucose and have additive effects with antidiabetes drugs.
Clinical research shows that whole soy diets and soy-based meals reduce fasting glucose levels in diabetic and non-diabetic individuals. Also, individuals following a soy-based meal replacement plan seem to require lower doses of sulfonylureas and metformin to manage blood glucose levels when compared with individuals following a diet plan recommended by the American Diabetes Association.

Likelihood Possible Evidence A

Antihypertensive Drugs

Theoretically soy protein may have additive effects with antihypertensive drugs and increase the risk of hypotension.
Although some contradictory research exists, most clinical evidence suggests that consuming soy protein modestly reduces systolic and diastolic blood pressure in individuals with prehypertension or hypertension.

Likelihood Possible Evidence A

Caffeine

Theoretically, soy might reduce the clearance of caffeine.
Soy contains genistein. Taking genistein 1 gram daily for 14 days seems to inhibit caffeine clearance and metabolism in healthy females. This effect has been attributed to inhibition of the cytochrome P450 1A2 (CYP1A2) enzyme, which is involved in caffeine metabolism. It is unclear if this effect occurs with the lower amounts of genistein found in soy.

Likelihood Possible Evidence D

Diuretic Drugs

Theoretically, soy might have additive effects when used with diuretic drugs.
Animal research suggests that genistein, a soy isoflavone, increases diuresis within 6 hours of subcutaneous administration in rats. The effects seem to be similar to those of furosemide. This effect has not been reported in humans.

Likelihood Possible Evidence D

Estrogens

Theoretically, soy might competitively inhibit the effects of estrogen replacement therapy.
Soy contains phytoestrogens and has been shown to have estrogenic activity in some patients. Although this has not been demonstrated in humans, theoretically, concomitant use of soy with estrogen replacement therapy might reduce the effects of the estrogen replacement therapy.

Likelihood Possible Evidence D

Levothyroxine (Synthroid, Others)

Soy products might reduce the absorption of levothyroxine in some patients.
Preliminary clinical research and a case report suggest that soy-based formulas inhibit the absorption of levothyroxine in infants with congenital hypothyroidism. A levothyroxine dosage increase may be needed for infants with congenital hypothyroidism while using soy-based formulas, and the dose may need to be reduced when soy-based formulas are no longer administered. However, in postmenopausal adults, clinical research shows that taking a single dose of soy extract containing isoflavones 60 mg along with levothyroxine does not affect the oral bioavailability of levothyroxine.

Likelihood Possible Evidence B

Progesterone

Theoretically, combining soy isoflavones with transdermal progesterone may worsen bone density.
Clinical research suggests that significant bone loss may occur in females with osteoporosis who receive a combination of transdermal progesterone with soy milk containing isoflavones when compared with placebo, soy milk alone, or progesterone alone.

Likelihood Possible Evidence A

Tamoxifen (Nolvadex)

Theoretically, estrogenic soy isoflavones might alter the effects of tamoxifen.
Laboratory research suggests that genistein and daidzen, isoflavones from soy, can antagonize the antitumor effects of tamoxifen under some circumstances; however, soy isoflavones might have different effects when used at different doses. A relatively low in vitro concentration of soy isoflavones such as 1 microM/L seems to interfere with tamoxifen, whereas high in vitro concentrations such as those >10 microM/L might actually enhance tamoxifen effects. People on a high-soy diet have soy isoflavones levels ranging from 0.1-6 microM/L. Until more is known, advise patients taking tamoxifen to avoid therapeutic use of soy products.

Likelihood Possible Evidence B

Warfarin (Coumadin)

Theoretically, soy might interfere with the effects of warfarin.
Soy milk has been reported to decrease the international normalized ratio (INR) in a patient taking warfarin. The mechanism of this interaction is not known. However, animal and in vitro research suggests that soy may also inhibit platelet aggregation. Dosing adjustments for warfarin may be necessary.

Likelihood Possible Evidence D

Antibiotic Drugs

Theoretically, antibiotics may decrease the activity of soy isoflavones.
Intestinal bacteria are responsible in part for converting soy isoflavones into their active forms. Antibiotics may decrease the amount of intestinal bacteria and decrease its ability to convert isoflavones.

Likelihood Possible Evidence D

Cytochrome P450 2C9 (Cyp2C9) Substrates

Soy might modestly induce CYP2C9 enzymes. However, this effect does not seem to be clinically significant.
In vitro research suggests that an unhydrolyzed soy extract might induce CYP2C9. However, the significance of this interaction is likely minimal. In healthy females taking a specific extract of soy (Genistein Soy Complex, Source Naturals), blood levels of losartan, a CYP2C9 substrate, were not significantly affected.

Likelihood Unlikely Evidence D

Monograph

Soy: Uses, Safety & Side Effects

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

The bottom line

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.

Scientific name: Glycine max
Family: Fabaceae
Part used: Bean (seed)
Common forms: Whole soybeans, soy milk, tofu, tempeh, edamame, soy protein powder, isoflavone capsules, soy lecithin

People commonly use it for

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

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

Safety at a glance

OverallUse caution

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

PregnancyLikely Safe

When used orally in amounts commonly found in foods.

Read the full pregnancy detail

BreastfeedingLikely 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 tim...

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

Soy comes from the soybean, the seed of the plant Glycine max, which is part of the legume (bean) family. Soybeans have been grown and eaten in East Asia for thousands of years and are now one of the most widely produced crops in the world.

Soy is found in many foods, such as tofu, tempeh, edamame, soy milk, and soy protein powders. It is also sold as dietary supplements, often standardized to contain plant compounds called isoflavones. People use soy both as a healthy source of plant protein and for possible health benefits like easing menopause symptoms and supporting heart health.

How it works

Soy contains isoflavones, mainly genistein and daidzein. These are sometimes called phytoestrogens because they are plant compounds that can weakly attach to estrogen receptors in the body. This is why soy is studied for menopause and other hormone-related effects.

Soy is also rich in high-quality protein, fiber, and healthy fats. The protein and fiber may help explain its possible effects on cholesterol. Some people can convert daidzein into a compound called equol, and this ability may affect how much benefit they get—though this is still being researched.

Much of what we know about how isoflavones act in the body comes from laboratory and animal studies, so the real-world effects in people are not fully understood.

Effectiveness

Does Soy work?

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

Evidence overview · 55 uses evaluated

11 Possibly effective 2 Leans ineffective 42 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.

Possibly Effective Chronic kidney disease (CKD)