Drug & supplement interaction

Soy + Caffeine (prescription drug)

Caffeine (prescription drug) brand names: Dextrophin, Caffeine.

Moderate Interaction
Medically reviewed by · Updated October 2026
The bottom line Moderate

Soy has a moderate interaction with Caffeine (prescription drug). Theoretically, soy might reduce the clearance of caffeine.

Read the full interaction report
SeverityModerate
LikelihoodPossible
EvidenceD
What do Severity, Likelihood & Evidence mean?
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Interaction report

Soy and Caffeine (prescription drug)

Here is the interaction we found between these two, with the evidence behind it.

Moderate

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.
Severity Moderate Likelihood Possible Evidence D

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.

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Here's the gist for your prescription caffeine. Your body clears caffeine mainly through a liver enzyme called CYP1A2. Soy contains a compound called genistein, and in one small study, a concentrated dose (1 gram of genistein daily for two weeks) appeared to slow that enzyme down. If caffeine is cleared more slowly, it can hang around longer, so you might notice more of its usual effects: jitteriness, a racing or pounding heart, trouble sleeping, or an upset stomach.

Now, the honest part: this is theoretical, based on how things work in the lab, not from strong real-world studies. The amount of genistein in everyday soy foods like tofu or edamame is much lower and likely won't matter much. It's the concentrated soy isoflavone supplements that are more of a question mark. If you're using those, just run it by your pharmacist or doctor first.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. 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

What These Ratings Mean

Every interaction above is graded three ways — here’s the key to each label.

Severity how clinically significant the interaction is
Major

Clinically significant. Avoid the combination, or use only under close professional supervision.

Moderate

Usually worth avoiding or managing — may need monitoring, a dose change, or timing apart.

Minor

Generally not serious. Be aware of it and mention it to your pharmacist.

Likelihood how strong the evidence is that the interaction actually happens in people
  • LikelyWell-controlled human studies have demonstrated the likely existence of this interaction.
  • ProbableInteraction 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.
  • PossibleInteraction 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.
  • UnlikelyInteraction has been demonstrated in animal or in lab research but has been shown not to occur in humans.
Evidence the quality of the studies behind the rating (graded A–D)
  • AHigh-quality meta-analysis (quantitative systematic review).
  • BCase-control study.
  • CConsensus.
  • DAnecdotal evidence.

These ratings are for information only. Never start, stop, or otherwise change your therapy before speaking with your provider.

Keep it in perspective

Soy Also Interacts With Other Medications

Soy has 9 major, 342 moderate, 260 minor known drug interactions in our database — the Caffeine (prescription drug) one above is one of them. If you take anything else, check it against the full list below.

Major 9 Moderate 342 Minor 260 No known interaction 2,219 (incl. Caffeine (prescription drug))
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.

Everything else you take

See Every Supplement That Interacts With Caffeine (prescription drug)

This page covers Soy only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Caffeine (prescription drug) page lists 208 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Ephedra (major), Grapefruit (major), Peyote (major) and Rauvolfia Vomitoria (major).

By severity: 7 major · 155 moderate · 46 minor.

From our pharmacist’s overview on the Caffeine (prescription drug) page

“Prescription caffeine is itself a stimulant, which is exactly why this list calls for genuine care rather than a quick skim. Seven of the 208 ingredients on file are rated major, and those deserve attention first.”

Reviewed by 2 · Jul 18, 2026

Open the Caffeine (prescription drug) 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. Your product may carry other ingredients that interact with Caffeine (prescription drug) too, on top of Soy — and those would not show on this page. Find your product and we’ll check every ingredient on its label:

How much people look this up

Where Soy and Caffeine (prescription drug) 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%

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

29 days ago today
Medication Caffeine (prescription drug)
Top 5%

#77 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.

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.

Read the full Soy monograph & all interactions
Medication

About Caffeine

What Is Caffeine Used For?

Brand names: Dextrophin, Caffeine

Caffeine citrate injection and oral solution are used for the short-term treatment of apnea of prematurity. This means pauses in breathing in premature infants. The label lists the age range as infants between 28 weeks and a later gestational age, and that range is cut off in the text provided.

Over-the-counter caffeine tablets, such as Diurex and the Stay Awake products, are taken by mouth by adults and older children. Their labels point to fatigue and drowsiness. Diurex directions also mention taking it while symptoms persist.

See full Caffeine drug information Caffeine NDC codes and packages
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
342Moderate
260Minor
2,218No known interaction
9 Major 342 Moderate 260 Minor 2,218 No interaction
Major

9 interactions

Moderate

342 interactions

Showing 60 of 342 moderate interactions — see all 342 on the Soy page.

Minor

260 interactions

Showing 60 of 260 minor interactions — see all 260 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 Caffeine (prescription drug), ranked by severity
Sources

Sources & How We Checked

Interaction details are evidence-graded and sourced from the Natural Medicines database. The medication overview comes from MedlinePlus.

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

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
Soy monograph › Uses, safety, and every drug interaction in one place Caffeine (prescription drug) supplement interactions › Every supplement checked against Caffeine (prescription drug), ranked by severity Caffeine drug information › The full plain-English guide to this medication Caffeine NDC codes and packages › Every package, labeler and price in the FDA directory Supplement interaction checker › Check any supplement or product against your medications Browse medications A–Z › Every drug we've checked against herbs & supplements Ask a pharmacist › Free, personal answer from our licensed team
Pharmacist Counseling Corner

Taking Soy and Caffeine (prescription drug) Together: Common Questions

Can you take Soy with Caffeine (prescription drug)?
There is a moderate interaction, so it may be acceptable with monitoring or timing changes — but check with your pharmacist first. Read the full details on this page and confirm with your pharmacist before combining them.
How serious is the Soy and Caffeine (prescription drug) interaction?
We rate it Moderate. This combination may require monitoring, a dose adjustment, or separating the times you take each one. Consult your pharmacist before using them together.

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

Still Have a Question About Caffeine (prescription drug) and Soy?

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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.