The short answer
Avoid bitter orange stimulant products during a linezolid course unless the prescriber agrees to monitor your blood pressure. Linezolid enhances the blood pressure effect of ephedrine-type stimulants, and p-synephrine in bitter orange is chemically related to ephedrine. At usual supplement doses p-synephrine did not raise blood pressure in people not taking linezolid, and the combination itself has not been studied, so the risk is a precaution rather than a measured effect.
What this answer covers
Bitter orange (Citrus aurantium) fruit or peel extracts standardised to p-synephrine, usually in weight-loss or pre-workout blends; amine content varies widely between brands.
- Supplement or preparation
- bitter orange
- Medication ingredient
- linezolid
Why the label applies by mechanism
Linezolid is a reversible MAO inhibitor that enhanced the blood pressure response to pseudoephedrine and phenylpropanolamine in volunteers, and its label requires blood pressure monitoring in anyone taking a sympathomimetic agent. p-Synephrine is a related amine, so the same caution is reasonable even though the label does not name it.
What the supplement studies found without linezolid
A 49 mg dose of p-synephrine produced no change in heart rate, systolic pressure or ECG in 18 healthy adults, and a 13 mg p-synephrine plus 176 mg caffeine product had no blood pressure effect in 23 overweight adults. Federal guidance calls the overall cardiovascular evidence inconclusive because other studies found increases.
Product content is the practical problem
An FDA analysis found bitter orange products containing more amines than a natural extract would provide, and most label claims for synephrine were inaccurate. A product with extra amines or added caffeine is closer to the labelled interaction than the tested 13 to 49 mg doses.
What to do
Linezolid courses are usually short. Pause bitter orange stimulant blends for the course, or ask the prescriber to check blood pressure if you continue. Seek urgent care for a severe headache, chest pain, pounding heartbeat or a very high reading.
Evidence and practical considerations
Side effects & toxicity
A conditional blood pressure precaution follows from the linezolid label's sympathomimetic warning and p-synephrine's structural relation to ephedrine; controlled studies of p-synephrine without linezolid did not raise blood pressure, and no exact-pair study exists.
- Exact scope
- p-Synephrine-standardised bitter orange extracts; amine content varies by product. with Linezolid tablets, oral suspension and intravenous injection (ZYVOX and generics); the reversible, nonselective MAO inhibition is a property of the drug at all routes.
- Medication form and route
- oral medication; intravenous medication; oral supplement
What remains uncertain
- Mechanism-based; contrary null results at usual doses without MAO inhibition; product amine content unreliable; no exact-pair data.
Factors that may matter: p-Synephrine and other amine content; Added caffeine or other stimulants; Existing high blood pressure; Dose.
Read the supporting source summaries
Source 1: current product label
dailymed.nlm.nih.gov · Source check Sep 22, 2026
Population: People prescribed linezolid
Enhanced pressor response to pseudoephedrine and phenylpropanolamine with linezolid in normotensive volunteers; blood pressure monitoring required in patients taking sympathomimetic agents or with uncontrolled hypertension.
How this applies: Exact linezolid (RxCUI 190376) at every marketed route; the label names tyramine, pseudoephedrine, phenylpropanolamine and serotonergic agents, not the supplements assessed here.
Bitter orange and p-synephrine are not named; applicability depends on whether p-synephrine behaves like the labelled indirect sympathomimetics, which the inspected trials question.
Source 2: original human study
pubmed.ncbi.nlm.nih.gov · Source check Sep 22, 2026
Population: Eighteen healthy adults, nine men and nine women.
No significant change in heart rate, systolic blood pressure, ECG or blood chemistry over 8 hours; a small 4.5 mmHg fall in diastolic pressure at 60 minutes; the authors concluded p-synephrine did not act as a stimulant at that dose.
How this applies: Contrary evidence on the stimulant premise at a common supplement dose; it does not test MAO-inhibited conditions.
Single dose without linezolid; healthy adults; caffeine intake varied; abstract only.
Source 3: original human study
pubmed.ncbi.nlm.nih.gov · Source check Sep 22, 2026
Population: Twenty-three mildly overweight adults.
No effect on heart rate, systolic, diastolic or mean arterial pressure was observed.
How this applies: Further null blood pressure data for a bitter orange plus caffeine product in people not taking an MAO inhibitor.
One-day exposure without linezolid; combined product; abstract only.
Source 4: federal supplement safety guidance
nccih.nih.gov · Source check Sep 22, 2026
Population: General consumer population; no medication co-use data
p-Synephrine is structurally similar to ephedrine but has different pharmacologic properties; evidence on cardiovascular effects is inconclusive, with some studies showing raised blood pressure and heart rate and others not; an FDA analysis found several products with more amines than expected and label amounts often inaccurate.
How this applies: Establishes the identity of the active amine, the uncertainty about its cardiovascular effect and the unreliability of product labelling.
Consumer summary; no linezolid or MAO inhibitor data.
Research assessment: · Open full citations ↗
Review and change history
- Publication status
- Published research summary
- Clinical review
- Not yet recorded
| Date | Update |
|---|---|
| Research summary published | |
| Article prepared | |
| Prepared exact linezolid and Citrus aurantium article from inspected current labeling and original sources, with uncertainty stated. |
Article revision: 37f461710106d49f
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.