Mephedrone, also known as 4-methylmethcathinone (4-MMC), or 4-methylephedrone, is a synthetic stimulant drug of the amphetamine and cathinone classes. Slang names include meph,drone, and MCAT. It is reportedly manufactured in China and is chemically similar to the cathinone compounds found in the khat plant of eastern Africa. It comes in the form of tablets or a powder, which users can swallow, snort or inject, producing similar effects to MDMA, amphetamines, and cocaine.

As well as producing the intended stimulant effects, negative side effects occur when mephedrone is used, with teeth grinding the most common. The metabolism of mephedrone has been studied in rats and humans, and the metabolites can be detected in urine after usage. Nothing is known about the potential neurotoxicity of mephedrone, but scientists have suggested possible dangers associated with its use based on its similarity to other drugs. Several people have died after consuming mephedrone, but some deaths that the media attributed to the drug were later determined to have been caused by other factors.