Mephedrone (4-methylmethcathinone) gained popularity across “recreational” drug scenes in the United Kingdom and Ireland during 2009. Although mephedrone was banned in both jurisdictions in 2010, the drug was subsequently sourced through street dealers. This qualitative study explores the simultaneous use of mephedrone and alcohol, among study participants who used mephedrone following legislative controls. Data were collected through semi-structured interviews with male and female respondents. The results suggest a three-tier classification system that describes users’ experiences with simultaneous use of mephedrone and alcohol. Most participants engaged in “heavy” alcohol use immediately prior to consuming mephedrone, and then reduced alcohol consumption as the effects of mephedrone were experienced during the drug episode. Spontaneous use of mephedrone often was associated with larger amounts of alcohol being consumed just prior to the mephedrone episode. The findings have the potential for informing socioepidemiological surveys as well as peer interventions to reduce harm associated with simultaneous drug use.