Drug & supplement interaction

Indole-3-carbinol + Theophylline

Theophylline brand names: T-Phyl, Duraphyl, Aerolate JR, Aerolate SR, Theo-Dur, and others.

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

Indole-3-carbinol has a moderate interaction with Theophylline. Theoretically, indole-3-carbinol might increase the metabolism of CYP1A2 substrates and lower serum concentrations.

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

Indole-3-carbinol and Theophylline

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

Moderate

CYTOCHROME P450 1A2 (CYP1A2) SUBSTRATES

Why this applies to Theophylline

Theophylline falls under CYTOCHROME P450 1A2 (CYP1A2) SUBSTRATES — the group Indole-3-carbinol interacts with.

Theoretically, indole-3-carbinol might increase the metabolism of CYP1A2 substrates and lower serum concentrations.
Animal research shows that indole-3-carbinol induces CYP1A2 enzymes.
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 theophylline. Your liver uses an enzyme called CYP1A2 to clear this medication out of your body. Indole-3-carbinol (I3C) is thought to speed up that enzyme, which could mean your body breaks down theophylline faster and your blood levels drift lower. For an asthma or COPD drug like this, lower levels can mean less protection, so you might notice more wheezing, shortness of breath, or chest tightness coming back.

One important thing: this concern comes only from lab and animal studies, not solid human data, so it's theoretical. Theophylline is also a narrow-window drug where levels matter, so don't change anything on your own. Just loop in your pharmacist or doctor before adding I3C.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. He YH, Friesen MD, Ruch RJ, Schut HA. Indole-3-carbinol as a chemopreventive agent in 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) carcinogenesis: inhibition of PhIP-DNA adduct formation, acceleration of PhIP metabolism, and induction of cytoch

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

Indole-3-carbinol Also Interacts With Other Medications

Indole-3-carbinol has 293 moderate known drug interactions in our database — the Theophylline one above is one of them. If you take anything else, check it against the full list below.

Moderate 293 No known interaction 2,537 (incl. Theophylline)
Taking anything else?

Check Another of Your Medications Against Indole-3-carbinol

Covers the 2,830 medications we’ve checked against Indole-3-carbinol. Pick one to open its full report.

From our Q&A

Questions About Indole-3-carbinol or Theophylline

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Indole-3-carbinol or Theophylline, 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 Theophylline

This page covers Indole-3-carbinol only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Theophylline page lists 126 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Ephedra (major), Sida Cordifolia (major), Adrafinil (moderate) and African Wild Potato (moderate).

By severity: 3 major · 89 moderate · 34 minor.

From our pharmacist’s overview on the Theophylline page

“Stop ephedra before anything else if you take theophylline (Theo-Dur, Slo-Bid, and others) for asthma or COPD. Both are stimulants, and together they raise the risk of serious heart and nervous system effects; Sida cordifolia, an herb that contains ephedrine, carries the same major rating.”

Reviewed by 2 · Jul 18, 2026

Open the Theophylline interaction page

One more smart check

Taking Indole-3-carbinol as Part of a Dietary Supplement Product? Check It for Interactions

We hold 287 real supplement products containing Indole-3-carbinol, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Indole-3-carbinol. Your product may carry other ingredients that interact with Theophylline too, on top of Indole-3-carbinol — 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 Indole-3-carbinol and Theophylline 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 Indole-3-carbinol
Top 25%

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

29 days ago today
Medication Theophylline
Steady interest

#1,948 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 Indole-3-carbinol

What is Indole-3-carbinol?

  • Estrogen and hormone balance support
  • Breast and cervical health
  • Prostate health
  • Antioxidant and 'detox' support
  • General cancer-prevention interest

Indole-3-carbinol (I3C) is a compound formed when you eat cruciferous vegetables like broccoli and cabbage, and it is sold as a supplement mainly for hormone-related and cell-protective effects. Most human evidence is preliminary or comes from lab and animal studies, so it should not be relied on to prevent or treat any disease. Talk to your pharmacist or doctor before using it, and avoid it in pregnancy and breastfeeding.

Read the full Indole-3-carbinol monograph & all interactions
Medication

About Theophylline

What Is Theophylline Used For?

Brand names: T-Phyl, Duraphyl, Aerolate JR, Aerolate SR, Theo-Dur, Slo-Bid, Theo-24, Uniphyl, Slo-phyllin Gyrocaps, Theolair, Theolair SR, Quibron-T/SR, Quibron-T, Aerolate III, Theo-X, Bronkodyl, Theoclear LA-130, Constant-T, Theoclear LA-260, Elixophyllin, Theovent, Theobid Jr Duracap, Respbid, Theobid Duracap

Theophylline — available as extended-release capsules (Theo-24), extended-release tablets, and oral solution (Elixophyllin) — is used to treat symptoms and reversible airflow obstruction caused by chronic asthma, emphysema, and chronic bronchitis.

All supported formulations share these indications. Theophylline is intended for patients with ongoing or recurring symptoms, not for sudden (acute) breathing attacks, which need faster-acting treatments.

See full Theophylline drug information
Keep checking

Other Drugs & Indole-3-carbinol

Browse every other medication we’ve checked against Indole-3-carbinol — both the ones with a known interaction and the ones without. Select any drug for the full detail.

0Major
293Moderate
0Minor
2,536No known interaction
293 Moderate 2,536 No interaction
Moderate

293 interactions

Showing 60 of 293 moderate interactions — see all 293 on the Indole-3-carbinol page.

No interaction 2,536 drugs checked — show the list

We also checked Indole-3-carbinol against these medications and found no known interaction in our sources. Open any page to confirm.

Showing the 60 most looked-up of 2,536 medications checked with no known interaction — see the full Indole-3-carbinol list.

See the full Indole-3-carbinol interactions page
See every supplement checked against Theophylline, 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
Indole-3-carbinol monograph › Uses, safety, and every drug interaction in one place Theophylline supplement interactions › Every supplement checked against Theophylline, ranked by severity Theophylline drug information › The full plain-English guide to this medication 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 Indole-3-carbinol and Theophylline Together: Common Questions

Can you take Indole-3-carbinol with Theophylline?
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 Indole-3-carbinol and Theophylline 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 Theophylline and Indole-3-carbinol?

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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.