Mephedrone (4-methylmethcathinone) is a synthetic cathinone that is used as a recreational drug. It has been available since 2007 but its availability and use increased significantly during 2009 and 2010. In this review article we will summarize the available literature on the sources, availability, and prevalence of the use of mephedrone. We will also discuss the pharmacology of mephedrone, the patterns of acute toxicity associated with its use, the reports of fatalities associated with its use, and the potential for mephedrone dependence. Copyright © 2011 John Wiley & Sons, Ltd.