Drug & supplement interaction

Indole-3-carbinol + Metoprolol

Metoprolol brand names: Lopressor, Toprol XL.

No Known Interaction
Medically reviewed by · Updated July 2026 · Pair last verified Sep 13, 2026
The bottom line No known interaction

We found no known interaction between Indole-3-carbinol and Metoprolol 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 label for Metoprolol states a food rule worth keeping to, and 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

Indole-3-carbinol and Metoprolol

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 Metoprolol and Indole-3-carbinol 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.

Indole-3-carbinol safety at a glance

Indole-3-carbinol overall Use caution Likely fine in food amounts, but supplement doses are less studied and should be used cautiously.
Pregnancy Avoid Not enough safety data and possible hormone effects, so concentrated supplements should be avoided.
Breastfeeding Avoid Safety has not been established, so supplement use is not recommended while breastfeeding.

Safety guidance is general; always confirm with your pharmacist or doctor for your situation.

Still wondering about combining Metoprolol and Indole-3-carbinol? Ask Dr. Brian Staiger, PharmD, BCPS directly ›
How we checked

Why No Interaction Is Listed for Metoprolol

Interactions in our licensed database are recorded against drug classes, not just single drug names. Metoprolol is filed under 6 classifications — including beta-blockers, antihypertensive drugs, cytochrome p450 2d6 (cyp2d6) substrates. Indole-3-carbinol has documented interactions with 3 drug classes — the most serious being anticoagulant/antiplatelet drugs (moderate), cytochrome p450 1a2 (cyp1a2) substrates (moderate) and estrogens (moderate) — and none of Metoprolol’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

Indole-3-carbinol Does Interact With Other Medications

Indole-3-carbinol has 294 moderate known drug interactions in our database — Metoprolol isn’t one of them. If you take anything else, check it against the full list below.

Moderate 294 No known interaction 2,536 (incl. Metoprolol)
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.

What to actually watch for

No Interaction Found — But Data Suggests Indole-3-carbinol and Metoprolol 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.

  • Diarrhea Additional detail

    Indole-3-carbinol

    “Orally, indole-3-carbinol increases gastrointestinal motility and has been associated with diarrhea.”

    Indole-3-carbinol · Natural Medicines adverse-effect record, reported in diarrhea.

    2 sources cited
    1. 93242. Reed GA, Peterson KS, Smith HJ, et al. A phase I study of indole-3-carbinol in women: tolerability and effects. Cancer Epidemiol Biomarkers Prev 2005;14:1953-60. PubMed
    2. 93243. Bradlow HL, Michnovicz JJ, Halper M, et al. Long-term responses of women to indole-3-carbinol or a high fiber diet. Cancer Epidemiol Biomarkers Prev 1994;3:591-5.

    Metoprolol

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

  • A skin rash Additional detail

    Indole-3-carbinol

    “Orally, indole-3-carbinol has been associated with reports of rash. A woman taking indole-3-carbinol 375 mg daily for treatment of systemic lupus erythematosus (SLE) developed a generalized maculopapular rash which resolved when indole-3-carbinol was discontinued and recurred when it was restarted.”

    Indole-3-carbinol · Natural Medicines adverse-effect record, reported in myasthenia gravis.

    2 sources cited
    1. 93242. Reed GA, Peterson KS, Smith HJ, et al. A phase I study of indole-3-carbinol in women: tolerability and effects. Cancer Epidemiol Biomarkers Prev 2005;14:1953-60. PubMed
    2. 93240. McAlindon TE, Gulin J, Chen T, et al. Indole-3-carbinol in women with SLE: effect on estrogen metabolism and disease activity. Lupus 2001;10:779-83. PubMed

    Metoprolol

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

  • Nausea Additional detail

    Indole-3-carbinol

    “Indole-3-carbinol has been associated with reports of unsteadiness and imbalance, especially at higher doses. An adult male taking 400 mg twice daily for treatment of recurrent respiratory papillomatosis developed imbalance and tremor after 10 days of treatment. This resolved when the dose was halved.”

    Indole-3-carbinol · Natural Medicines adverse-effect record, reported in myasthenia gravis.

    2 sources cited
    1. 7172. Rosen CA, Woodson GE, Thompson JW, et al. Preliminary results of the use of indole-3-carbinol for recurrent respiratory papillomatosis. Otolaryngol Head Neck Surg 1998;118:810-5. PubMed
    2. 93238. Anon. Indole-3-carbinol. Monograph. Alternative Medicine Review 2005;10(4):337-42.

    Metoprolol

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

Reported for Indole-3-carbinol but not commonly for Metoprolol: unsteadiness and tremor or shakiness.

Effects for Metoprolol come from the ADVERSE REACTIONS section of its FDA label; effects for Indole-3-carbinol 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.

How to take them

Some Metoprolol Products Have a Food Rule — Indole-3-carbinol Should Not Break It

At least one FDA label for a product containing Metoprolol says to take it with food. If you take Indole-3-carbinol on an empty stomach out of habit, keep them separate — and take Metoprolol with a meal where the label says to.

This may not be true of your version. Food instructions belong to the product, not the ingredient: two Metoprolol products can carry different directions, and extended-release forms often differ from immediate-release ones. The label we read is quoted below — check the directions on your own box or bottle, or ask your pharmacist, for how to take the exact product you were given.

Administer once daily with food or after a meal.

From the Dosage and Administration section of the FDA label we read for Metoprolol — where that label names a specific product, the instruction is that product's. Read the label on DailyMed ›

A food rule is not an interaction — it is about how much of the medicine you absorb. The directions that came with your own product, and your pharmacist, outrank anything on this page.

From our Q&A

Questions About Indole-3-carbinol or Metoprolol

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 Metoprolol, 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 Metoprolol

This page covers Indole-3-carbinol only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Metoprolol page lists 183 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), American Hellebore (major), American Mistletoe (major), Indian Snakeroot (major) and Tyramine (major).

By severity: 5 major · 152 moderate · 26 minor.

From our pharmacist’s overview on the Metoprolol page

“With metoprolol (Lopressor, Toprol XL), a beta-blocker for high blood pressure and heart problems, these interactions deserve genuine care, starting with the five rated major. Most entries pull blood pressure one way or the other: many supplements add to metoprolol's lowering effect and can drop pressure too far, while a few, tyramine…”

Reviewed by 2 · Jul 18, 2026

Open the Metoprolol 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. Even though Indole-3-carbinol itself has no known interaction with Metoprolol, 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 Indole-3-carbinol and Metoprolol 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%

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

29 days ago today
Medication Metoprolol
Top 10

#7 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 Indole-3-carbinol reference on this page ↓
  • Freshness: we automatically re-check this combination every week — this pair was last verified September 13, 2026. The Indole-3-carbinol and Metoprolol records this page draws on were last updated July 10, 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 .
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.

Brassicaceae · Derived from glucosinolates found in cruciferous vegetables (broccoli, cabbage, Brussels sprouts, cauliflower) · Capsules, tablets, softgels; sometimes combined with or compared to diindolylmethane (DIM)

An interaction check asks whether these two react with each other — it does not ask whether Indole-3-carbinol is a good idea for someone in your situation. Here is what our Indole-3-carbinol record says about it on its own.

Indole-3-carbinol: dosing

There is no officially established or standardized dose for I3C. Different products and studies have used different amounts, and there is no agreed-upon 'best' dose.The safest approach is to follow the directions on the product label and not exceed them. They can help you decide whether I3C is appropriate for you.

From our Indole-3-carbinol monograph — the full record covers uses, side effects and every documented interaction.

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

About Metoprolol

What Is Metoprolol Used For?

Brand names: Lopressor, Toprol XL

Metoprolol is used to treat several heart and blood pressure conditions. Metoprolol succinate extended-release tablets (including Toprol-XL) are approved for high blood pressure, angina pectoris (chest pain from the heart), and heart failure. Metoprolol tartrate tablets (including Lopressor) are approved for high blood pressure, angina, and — when used alongside intravenous metoprolol — to reduce the risk of cardiovascular death after a definite or suspected heart attack.

Metoprolol tartrate injection (intravenous form) is used in hemodynamically stable patients with a definite or suspected acute heart attack to reduce cardiovascular death, and is followed by oral metoprolol therapy. Lowering blood pressure with metoprolol reduces the risk of strokes and heart attacks.

Most-Reported Side Effects for Metoprolol

From FAERS, the FDA’s public side-effect reporting system (0 reports, all brands). Reports are voluntary and are not proof the drug caused the effect.

Fatigue 23,416 reports
Dyspnea 20,183 reports
Diarrhea 19,912 reports
Nausea 19,659 reports
Dizziness 16,726 reports
See full Metoprolol 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
294Moderate
0Minor
2,535No known interaction
294 Moderate 2,535 No interaction
Moderate

294 interactions

Showing 60 of 294 moderate interactions — see all 294 on the Indole-3-carbinol page.

No interaction 2,535 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 2,535 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 Metoprolol, ranked by severity
Evidence & sources

Indole-3-carbinol References

The 9 references that drive our Indole-3-carbinol 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.

  1. Rosen CA, Woodson GE, Thompson JW, et al. Preliminary results of the use of indole-3-carbinol for recurrent respiratory papillomatosis. Otolaryngol Head Neck Surg 1998;118:810-5. PubMed
  2. Bell MC, Crowley-Nowick P, Bradlow HL, et al. Placebo-controlled trial of indole-3-carbinol in the treatment of CIN. Gynecol Oncol 2000;78:123-9. PubMed
  3. 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
  4. Kim, Y. S. and Milner, J. A. Targets for indole-3-carbinol in cancer prevention. J.Nutr.Biochem. 2005;16(2):65-73. PubMed
  5. Anon. Indole-3-carbinol. Monograph. Alternative Medicine Review 2005;10(4):337-42.
  6. McAlindon TE, Gulin J, Chen T, et al. Indole-3-carbinol in women with SLE: effect on estrogen metabolism and disease activity. Lupus 2001;10:779-83. PubMed
  7. Reed GA, Peterson KS, Smith HJ, et al. A phase I study of indole-3-carbinol in women: tolerability and effects. Cancer Epidemiol Biomarkers Prev 2005;14:1953-60. PubMed
  8. Bradlow HL, Michnovicz JJ, Halper M, et al. Long-term responses of women to indole-3-carbinol or a high fiber diet. Cancer Epidemiol Biomarkers Prev 1994;3:591-5.
  9. Paliwal P, Chauhan G, Gautam D, Dash D, Patne SCU, Krishnamurthy S. Indole-3-carbinol improves neurobehavioral symptoms in a cerebral ischemic stroke model. Naunyn Schmiedebergs Arch Pharmacol. 2018;391(6):613-625. PubMed

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 Indole-3-carbinol and Metoprolol Together: Common Questions

Is it safe to take Indole-3-carbinol with Metoprolol?
We do not list a known interaction between Indole-3-carbinol and Metoprolol. 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 Indole-3-carbinol and Metoprolol have any of the same side effects?
Yes — our sources link each of them separately to 3 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.
Should I take Indole-3-carbinol and Metoprolol at the same time of day?
At least one FDA label for a product containing Metoprolol says to take it with food. If you take Indole-3-carbinol on an empty stomach out of habit, keep them separate and take Metoprolol with a meal where the label says to. Food instructions belong to the product rather than the ingredient — two Metoprolol products can differ — so check the directions on your own box. This is about absorption, not an interaction.
How was the Indole-3-carbinol and Metoprolol combination checked?
Interactions in our licensed database are recorded against drug classes. Metoprolol is filed under 6 classifications, and Indole-3-carbinol has documented interactions with 3 drug classes — none of Metoprolol'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 Indole-3-carbinol interact with any other medications?
Yes. Indole-3-carbinol has 294 documented drug interactions in our database — Metoprolol 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 Metoprolol interact with any supplements?
Yes. Metoprolol has documented interactions with 183 supplements in our database — Indole-3-carbinol is not one of them. The Metoprolol 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

Keep Exploring

Indole-3-carbinol monograph Uses, safety profile, and every drug interaction in one place Metoprolol drug information The full plain-English guide to this medication Metoprolol supplement interactions Every supplement checked against Metoprolol, ranked by severity Supplement interaction checker Check any supplement or product against your medications Browse medications A–Z Every drug we’ve checked against herbs & supplements References The 9 citations behind this page Ask a pharmacist Free, personal answer from our licensed team

Still Have a Question About Metoprolol 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.