Psychotic disorders among inpatients with abuse of cannabis, amphetamine and opiates. Do dopaminergic stimulants facilitate psychiatric illness?

We have studied the occurrence of dual diagnoses (psychoses as well as abuse of either amphetamine, cannabis or opiates) during a 15-year period, among patients treated at Huddinge Hospital, Stockholm, Sweden. The purpose of the study is to evaluate if the different drugs were coupled to different rates of psychiatric co-morbidity. During the period in question, 461, 425 and 371 different patients respectively had been admitted at least once due to dependency on amphetamine, cannabis and opiates. Approximately 30% of the patients with a pure abuse of amphetamine or cannabis and less than 6% of the opiate abusers had been diagnosed at least once with any of the psychoses studied. Comparing the frequency of psychoses among mixed and pure abusers of illegal drugs, with and without a concomitant abuse of alcohol, we found that the co-morbidity rate for mixed opiate abusers increased significantly from 7.2 to 20.2% when alcohol abuse was also present. For abusers of amphetamine and cannabis (both pure and mixed), no differences in co-morbidity rates were seen when an abuse of alcohol was added to that of the drugs. It is difficult to find an explanation for the significant difference between the co-morbidity of pure abuse of amphetamine or cannabis on the one hand and opiates on the other. In conclusion, our findings show that the distribution of psychotic illness is high among abusers of amphetamine and cannabis, in contrast to the generally lower co-morbidity among abusers of opiates. Although these findings are consistent with earlier studies that have shown a propensity for developing psychoses among abusers of amphetamine and cannabis, one should bear in mind that this study is based on inpatients, and is not necessarily representative for all abusers of the drugs in question.