Methylsynephrine is a chemical that is made in the lab. It is found in some dietary supplements. According to the US Food and Drug Administration (FDA), methylsynephrine does not meet the definition of a dietary supplement. Also, it is banned by the World Anti-Doping Agency (WADA) for use during competitive sports, and by the Department of Defense (DOD) for use by military personnel.
Methylsynephrine is commonly used for weight loss, athletic performance, lung problems, and other uses, but there is no good scientific evidence to support these uses.