The short answer
Guarana contributes caffeine, so have your pharmacist review the total amount before taking it with isocarboxazid. Marplan warns against excessive caffeine. The evidence supports a conditional stimulant and blood-pressure concern, not a proven serotonin-syndrome or QT interaction.
What this answer covers
Oral Paullinia cupana caffeine-containing preparations, usually seed products. The caffeine content of an unidentified formulation cannot be inferred from the name alone.
- Supplement or preparation
- Paullinia cupana
- Medication ingredient
- isocarboxazid
Why guarana counts as caffeine
Guarana naturally contains caffeine, even when a label lists only the herb. Marplan warns against excessive caffeine from any source. There is no validated guarana dose or general caffeine threshold that establishes safety with this medication.
What the research can and cannot show
A small trial found higher blood pressure and heart rate after ephedra-guarana combinations. It tested healthy adults, not Marplan users, and cannot identify guarana alone as the cause. Specific claims of serotonin syndrome or QT prolongation remain unsupported for this pair.
Check your total intake
Bring the complete product label to your pharmacist. Include coffee, tea, energy drinks and other stimulant supplements when reviewing intake. Do not rely on taking guarana at a different time to make excessive caffeine safe.
When to seek medical care
A sudden severe headache, chest pain, pounding heartbeat, sweating or neck stiffness needs urgent medical assessment. Do not change prescribed isocarboxazid without your prescriber.
Evidence and practical considerations
Side effects & toxicity
Guarana contributes caffeine, so have your pharmacist review the total amount before taking it with isocarboxazid. Marplan warns against excessive caffeine. The evidence supports a conditional stimulant and blood-pressure concern, not a proven serotonin-syndrome or QT interaction.
- Exact scope
- Oral Paullinia cupana caffeine-containing preparations, usually seed products. The caffeine content of an unidentified formulation cannot be inferred from the name alone. with isocarboxazid, RxCUI 6011 IN; oral MARPLAN tablets.
- Medication form and route
- Oral isocarboxazid; oral supplement
What remains uncertain
- The precaution depends on caffeine exposure. No exact-pair clinical trial, validated safe guarana dose, serotonin-syndrome finding or QT-prolongation finding was identified. Ephedra-guarana combination studies cannot isolate guarana.
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: Federal ingredient information
ods.od.nih.gov · Source check Sep 10, 2026
Population: Consumers of caffeine and botanical dietary supplements.
Guarana and tea can contribute caffeine, and a botanical ingredient list may omit the amount of caffeine. Caffeine has stimulant effects.
How this applies: General healthy-adult caffeine limits are not safety limits for patients receiving MAOIs. No exact guarana-MAOI trial is supplied.
General healthy-adult caffeine limits are not safety limits for patients receiving MAOIs. No exact guarana-MAOI trial is supplied.
Source 3: 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: 01ebf9daa1b358ff
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.