From "Special K" to "Special M": the evolution of the recreational use of ketamine and methoxetamine

This article reviews the recreational use of ketamine ("Special K"; KET) and explores the recent diffusion of its new derivative methoxetamine ("Special M"; MXE). The literature search on the nonclinical/recreational use of KET and MXE was carried out in a range of medical databases. Considering the limitations of peer-reviewed information, data were integrated with a qualitative assessment of a range of websites, drug fora, and other online resources including e-newsgroups, chat rooms, mailing lists, e-newsletters, and bulletin boards. The recreational use of KET has started since its discovery in 1962. This was due to its rapid onset, short duration of action, and peculiar psychotropic effects ("K-hole"). The latter effect ranges from confusion to dissociation and depersonalization (near-death experience). However, KET abuse is often associated with physical and psychological side effects, of which the worst is urological/bladder toxicity. Recently, MXE has emerged as a legal and "bladder-friendly" KET alternative. MXE presents with the same dissociative effect of KET, but with slower onset and longer duration of action. However, MXE seems to be associated with worse side effects than KET, ranging from mood disturbances/suicidal attempts to acute cerebellar toxicity. After 50 years of its discovery, KET has led to the emergence of MXE. However, this latter derivative does not appear to be a safer alternative to KET itself.