3-Methylmethcathinone (also known as 3-MMC or metaphedrone) is a novel stimulant-entactogen substance of the cathinone class that produces a mixture of classical stimulant and entactogenic effects when administered. It is a member of a group known as the substituted cathinones, all of which are derivatives of cathinone, the principal active component in the khat plant (Cathulla edullis) of eastern Africa.

As with many of its research chemical cathinone predecessors, 3-MMC is known to come in the form of either a white powder or crystallized shards which users can ingest to produce a powerful, fast-acting but short-lived euphoric stimulant-entactogen effects, particularly when they are insufflated, vaporized or injected.

It has gained notoriety for its associated tendency to induce compulsive redosing and addictive behaviors in a seemingly significant percentage of its users as well the ability to readily induce paranoid, anxiety, various delusional states and stimulant psychosis when taken too frequently, in excessive amounts, or over extended periods of time.

Limited data exists about the pharmacological properties, metabolism, and toxicity of 3-MMC, and it has little history of human usage. 3-MMC first became available on the online research chemical market, shortly after the banning of mephedrone. It is a rominent example of a contemporary designer drug specifically chosen to mimic and/or replace the functional and structural features of its recently-controlled predecessors.