This case report describes an acute overdose in a female patient with the serotonin mixed agonist-antagonist m-chlorophenylpiperazine (mCPP), a new synthetic drug that is also a metabolite of the antidepressant trazodone. Following ingestion of three multi-coloured tablets, she developed anxiety, agitation, drowsiness, flushing, visual disturbances and tachycardia. The mCPP concentration was 320 ng/mL in plasma and 2300 ng/mL in urine. Amphetamine (40 ng/mL), benzoylecgonine (47 ng/mL) and alcohol (0.7 g/L) were also detected in plasma. The concentration of mCPP in plasma was approximately six times higher than the usual concentration measured in patients under trazodone treatment (26-108 ng/mL, average 56 ng/mL). However, one should be careful to link the observed symptoms to the use of mCPP only as the other drugs that have also been taken or an interaction between the drugs could also have played a role.