Methylsynephrine (also known as oxilofrine or p-hydroxyephedrine) is sometimes used as an ingredient in dietary supplement products, but the Food and Drug Administration (FDA) says it “does not meet the statutory definition of a dietary supplement ingredient.” Therefore, products containing methylsynephrine are “adulterated” that is, unsafe and can’t be marketed legally as dietary supplements in the U.S.
Methylsynephrine is prohibited in sport because it’s an approved pharmaceutical drug in some countries (but not currently in the U.S.), and it’s a stimulant that increases blood pressure and affects heart rate. One study found that some supplements contain methylsynephrine in amounts equal to or greater than pharmaceutical doses. The consequences of taking methylsynephrine in large amounts or in combination with other stimulants aren’t entirely known, but one product containing this ingredient and other stimulants has been linked to nausea, vomiting, agitation, increased heart rate, chest pain, and cardiac arrest.
For more information, please see FDA’s information page on “Methylsynephrine in Dietary Supplements.”
Updated 27 April 2016