3-MMC Crystal 3-Methylmethcathinone, also known as 3-Mephedrone – is a designer drug from the substituted cathinone family, with Empathogen-entactogen effects. 3-MMC is closely related in structure to the popular drug mephedrone (4-MMC). Available with a purity of 98% +, it is suitable as a replacement for mephedrone.