3-Fluoromethcathinone (also known as 3-FMC) is a chemical compound of the phenethylamine, amphetamine, and cathinone classes that has been sold online as a designer drug. It is a structural isomer of flephedrone (4-fluoromethcathinone). 3-Fluoroisomethcathinone is produced as a by-product when 3-FMC is synthesized, the activity of this compound is unknown.