The Discriminative‐Stimulus Effects of Mephedrone in Comparison with Other Drugs of Abuse

Abstract

Mephedrone (4‐methylmethcathinone) is one of the major constituents of the recreational drug, “bath salts”. It is a synthetic cathinone and potent psychostimulant that has been reported to cause auditory and visual hallucinations. The purpose of this study was to compare the discriminative stimulus effects of mephedrone alone with those of other prototypical drugs of abuse, such as cocaine, delta‐9‐tetrahydrocannabinol (THC), phencyclidine (PCP), and 2,5‐dimethoxy‐4‐iodoamphetamine (DOI). Rats were trained to discriminate an intraperitoneal injection of mephedrone from saline under a fixed‐ratio 20 schedule of food presentation. The final training dose of mephedrone was 3.2 mg/kg and it was reliably discriminated from saline by all subjects. Following training, substitution tests indicated that cocaine (0.56‐32 mg/kg) fully substituted for mephedrone (0.32‐10 mg/kg) by producing over 80% mephedrone‐lever responding, whereas THC (0.56‐10 mg/kg), PCP (1‐5.6 mg/kg) and DOI(0.1‐1 mg/kg) produced a maximum of 73%, 30% and 50% mephedrone‐lever responding, respectively. Only THC produced dose‐dependent rate‐decreasing effects (蠅 20% decrease in response rate compared to THC vehicle). These results indicate that the discriminative stimulus effects of mephedrone most closely approximate those for the stimulant drug, cocaine, and are only modestly similar to THC.