Methylsynephrine (Oxilofrine)
Methylsynephrine (oxilofrine / p-hydroxyephedrine) is a synthetic sympathomimetic stimulant historically used as a cardiac drug in a few countries and sold illicitly in weight-loss and pre-workout supplements. It is more potent than synephrine and is not a legal dietary-supplement ingredient in the US. It raises heart rate and blood pressure, has caused adverse-event reports, and is banned in sport.
01 Overview
Methylsynephrine, also known as oxilofrine or para-hydroxyephedrine, is a synthetic beta-hydroxylated phenethylamine related to synephrine and ephedrine. In a handful of countries it has been used clinically as a cardiac stimulant for hypotension. It is not an approved drug or a lawful dietary ingredient in the United States, but has repeatedly been found spiked into weight-loss and pre-workout supplements, sometimes undeclared.
As a sympathomimetic it raises heart rate, blood pressure and metabolic rate, and is marketed for energy and fat loss. Because it is more potent than synephrine and often present at variable, undeclared doses, it has been associated with adverse cardiovascular event reports. The FDA has warned against products containing it, and it is prohibited in sport by WADA. Human pharmacological data are limited and mostly old.
02 Mechanism
Synthetic sympathomimetic amine that stimulates adrenergic receptors and promotes noradrenaline activity, raising heart rate, blood pressure, metabolic rate and alertness; more potent than synephrine.
03 Dosing
| Tier | Dose | Route | Notes |
|---|---|---|---|
| Supplement (illicit) | 20–40 mg | Oral | Doses found in spiked supplements vary widely and are often undeclared; not a legitimate or standardised dose. |
| Higher spiked dose | 40–100 mg/day | Oral | Higher amounts found in some products; cardiovascular risk rises with dose and stacking. |
04 Effects
| Effect | Magnitude | Evidence | |
|---|---|---|---|
| Stimulant energyIncreased alertness and perceived energy, marketed as a pre-workout effect. | moderate | Anecdotal | |
| ThermogenesisClaimed increase in metabolic rate for fat loss; human efficacy data are limited. | modest, unproven | Anecdotal |
05 Side effects
| Effect | Severity | Frequency | Evidence | Countermeasures |
|---|---|---|---|---|
| Raised heart rate and blood pressureElevated heart rate and blood pressure; adverse cardiovascular event reports have been linked to spiked supplements. | Moderate | Common | Observational | |
| Palpitations and arrhythmiaPalpitations and, in reports, more serious arrhythmic events, especially with high or undeclared doses and stimulant stacking. | Severe | Uncommon | Observational | |
| Anxiety and insomniaStimulant-related anxiety, jitteriness and insomnia. | Mild | Common | Anecdotal |