Mephedrone (4-MMC) is the most popular of the cathinone derivatives used as recreational drugs (colloquially called “legal highs”). It elicits stimulant and emphatogenic effects similar to amphetamines, cocaine and ecstasy. This review surveys the current state of knowledge regarding the pharmacological properties of mephedrone; special emphasis is given to its potency as psychoactive and symphatomimetic drug. It also addresses the negative consequences of using mep­hedrone products.