The short answer
Indole-3-carbinol could change ropinirole clearance because it increased a relevant liver-enzyme signal in a small human study. Reduced ropinirole levels or benefit have not been directly demonstrated. Review starting or stopping the supplement with your prescriber.
What this answer covers
Oral indole-3-carbinol supplements studied at 400-800 mg daily; DIM supplements and ordinary cruciferous vegetables are different exposures.
- Supplement or preparation
- Indole-3-carbinol
- Medication ingredient
- ropinirole
What the human study measured
Seventeen women took indole-3-carbinol after a placebo run-in period. At the higher tested dose, caffeine-based measurements showed increased activity of CYP1A2 in most participants. The study measured enzyme activity, not ropinirole concentrations.
Why that could matter for ropinirole
CYP1A2 is the main enzyme involved in clearing ropinirole. More enzyme activity could plausibly increase clearance, but the amount of any change and its effect on symptoms cannot be calculated from this study.
Do not confuse clearance with absorption
The concern is a possible change in liver metabolism, not demonstrated blockage of ropinirole absorption. The supplement study also does not justify avoiding ordinary vegetables or treating DIM as an identical product.
How to handle a planned change
Tell your pharmacist or prescriber before starting or stopping the supplement, and bring the product label. Report a clear change in symptom control or side effects. These sources do not establish a protective spacing interval or a standard ropinirole dose adjustment for this supplement.
Evidence and practical considerations
Absorption & effectiveness
A human CYP1A2 induction signal supports a possible interaction mechanism, but reduced ropinirole effectiveness or absorption remains unproven.
- Exact scope
- Oral indole-3-carbinol supplements studied at 400-800 mg daily; DIM supplements and ordinary cruciferous vegetables are different exposures. with Oral immediate-release ropinirole; hydrochloride salt expressed as equivalent free base in the inspected label.
- Medication form and route
- oral ropinirole; supplement preparation and route described in scope
- Timing or duration
- No exact-pair safe duration or protective spacing interval established.
What remains uncertain
- One small sequential-dose study in women used caffeine phenotyping, not ropinirole measurements or clinical treatment response.
Factors that may matter: supplement dose; starting or stopping repeated use.
Read the supporting source summaries
Source 1: current product label
dailymed.nlm.nih.gov · Source check Sep 10, 2026
Population: People prescribed oral immediate-release ropinirole tablets for Parkinson disease or primary restless legs syndrome.
Ropinirole can cause somnolence, sudden sleep episodes and orthostatic hypotension. Concomitant sedating medicines or alcohol can increase sleepiness risk. CYP1A2 is its major metabolic enzyme; inhibitors and inducers may alter clearance. Ciprofloxacin increased exposure, whereas theophylline did not. Cigarette smokers had lower dose-normalized exposure than nonsmokers in a small RLS comparison.
How this applies: Exact oral ropinirole risk and metabolic context; section 11 justifies hydrochloride-to-free-base active-moiety identity only.
None of these ten supplement pairs is directly tested in this label. Cigarette smoking is not interchangeable with oral cannabis or isolated CBD; ciprofloxacin results are not caffeine results. No extended-release kinetic equivalence assumed.
Source 2: phase 1 human enzyme-phenotyping study
pubmed.ncbi.nlm.nih.gov · Source check Sep 10, 2026
Population: 17 women at high risk for breast cancer.
Caffeine phenotyping showed increased CYP1A2 activity in 94% of participants; the abstract reports a mean 4.1-fold increase. Doses were generally tolerated.
How this applies: A human induction signal relevant to a CYP1A2 substrate; cannot predict the size or clinical effect of a ropinirole interaction.
No ropinirole, clinical efficacy outcome or direct measurement of ropinirole absorption. Nonrandomized sequential doses in a small selected population.
Research assessment: · Open full citations ↗
Review and change history
- Publication status
- Published research summary
- Clinical review
- Not yet recorded
| Date | Update |
|---|---|
| Article prepared | |
| Sources inspected and exact current claim adjudicated; no clinical review asserted. | |
| Research summary published |
Article revision: ef50b96142e6544e
This guide brings together the evidence records used by our interaction checker. Each finding retains its own preparation limits, research date, and source summaries.
Full citations require verification. Reading this answer and the source summaries does not.
Taking other supplements or medications?
Use the checker to explore your other combinations. Ask a pharmacist to review the exact products, amounts and medical conditions in your complete list.
Open the interaction checkerInformation, not medical advice. Do not change prescribed treatment based on this guide.