The short answer
Avoid ephedrine-alkaloid-containing Ephedra sinica while taking isocarboxazid. Marplan contraindicates sympathomimetics, and oral ephedrine labeling prohibits use with an MAOI. The strongest supported concern is a dangerous blood-pressure response.
What this answer covers
Oral Ephedra sinica stem or branch preparations containing ephedrine-type alkaloids. Root, other species, purified ephedrine salts and purported alkaloid-free products are not interchangeable.
- Supplement or preparation
- Ephedra sinica
- Medication ingredient
- isocarboxazid
Why avoidance matters
Marplan warns against sympathomimetic drugs. Ephedra sinica stems and branches can supply ephedrine alkaloids. This constituent link supports avoidance, although it does not establish an event rate for a specific botanical product.
What human research shows
A small study of ephedra and guarana combinations found increased blood pressure and heart rate in healthy adults. It did not include isocarboxazid or isolate either herb. It cannot establish serotonin syndrome or QT prolongation from this pair.
Check every ingredient
Do not use an ephedrine-alkaloid product with Marplan. The oral ephedrine label also prohibits use for two weeks after stopping an MAOI; ask your prescriber about medication changes rather than planning your own washout. Hour-by-hour separation is not a workaround.
Symptoms requiring urgent care
Get urgent medical help for a severe headache, chest pain, palpitations or marked sweating. Ephedra also has serious risks on its own, and ephedrine alkaloids are prohibited in U.S. dietary supplements.
Evidence and practical considerations
Side effects & toxicity
Avoid ephedrine-alkaloid-containing Ephedra sinica while taking isocarboxazid. Marplan contraindicates sympathomimetics, and oral ephedrine labeling prohibits use with an MAOI. The strongest supported concern is a dangerous blood-pressure response.
- Exact scope
- Oral Ephedra sinica stem or branch preparations containing ephedrine-type alkaloids. Root, other species, purified ephedrine salts and purported alkaloid-free products are not interchangeable. with isocarboxazid, RxCUI 6011 IN; oral MARPLAN tablets.
- Medication form and route
- Oral isocarboxazid; oral supplement
What remains uncertain
- The blood-pressure precaution applies to ephedrine-alkaloid-containing preparations. An exact-pair clinical event rate is unknown. The inspected evidence does not establish serotonin syndrome, QT prolongation or a specific arrhythmia mechanism from this pair.
Factors that may matter: Exact product composition and dose; Other medicines and supplements.
Read the supporting source summaries
Source 1: Current U.S. prescribing information
dailymed.nlm.nih.gov · Source check Sep 10, 2026
Population: Patients prescribed oral isocarboxazid tablets.
Phenylalanine is named among substances that may precipitate hypertension and headache. Sympathomimetics, some CNS depressants and excessive caffeine are contraindicated. The label describes high-tyramine hypertensive crises and warns about drowsiness, hypotension and impaired driving.
How this applies: Exact isocarboxazid authority. Botanical applicability must be assessed from the relevant constituent or sedating effect rather than a botanical name alone.
The label does not quantify these botanical pair risks or give a universally safe supplement dose.
Source 2: U.S. oral-product labeling
dailymed.nlm.nih.gov · Source check Sep 10, 2026
Population: Users of the labeled oral ephedrine hydrochloride product.
Do not use during prescription MAOI treatment or for two weeks after stopping an MAOI. The label also warns about blood-pressure and heart-rate increases.
How this applies: Constituent-level warning applicable to ephedrine-containing ephedra preparations; no botanical coadministration trial is claimed.
The source concerns a specific ephedrine salt and product. The botanical bridge depends on actual ephedrine-alkaloid content, not shared wording alone.
Source 3: Federal safety information
nccih.nih.gov · Source check Sep 10, 2026
Population: Users of ephedra-containing products.
NCCIH describes serious cardiovascular and neurologic risks and the FDA prohibition on ephedrine alkaloids in dietary supplements.
How this applies: Does not establish a measured interaction rate with isocarboxazid. Does not cover every ephedra species or plant part.
Does not establish a measured interaction rate with isocarboxazid. Does not cover every ephedra species or plant part.
Source 4: Original randomized human study
ebi.ac.uk · Source check Sep 10, 2026
Population: 16 healthy adults, including eight women.
Both active combinations increased heart rate and blood pressure.
How this applies: Abstract only. No isocarboxazid and no single-botanical arm. Cannot isolate guarana, establish the exact Ephedra species or quantify an MAOI interaction; not proof of serotonin syndrome or QT prolongation.
Abstract only. No isocarboxazid and no single-botanical arm. Cannot isolate guarana, establish the exact Ephedra species or quantify an MAOI interaction; not proof of serotonin syndrome or QT prolongation.
Research assessment: · Open full citations ↗
Review and change history
- Publication status
- Published research summary
- Clinical review
- Not yet recorded
| Date | Update |
|---|---|
| Article prepared | |
| Sources checked and article drafted. | |
| Clarified the distinction between the original dataset statement and the narrower source-supported precaution, and edited evidence limitations for readers. | |
| Research summary published |
Article revision: 2a7ef7401c063a62
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.