3-MMC, or 3-Methylmethcathinone, is a molecule of the substituted cathinone class. Cathinones are a sub-category of amphetamines, sharing share the core amphetamine structure of a phenyl ring bound to an amino (NH2) group through an ethyl chain and an additional methyl substitution at Rα.

3-MMC and other cathinones are differentiated by their ketone substitution on the beta carbon of the amphetamine skeleton, meaning they are β-keto-amphetamines. 3-MMC has two methyl substitutions on its cathinone skeleton, one at R3 of the phenyl ring, and a second at the nitrogen group RN. 3-MMC is analogous to mephedrone; it is identical in structure expect for the placement of the methyl group at R3 instead of R4.