Which drugs cause overdose among opiate misusers? Study of personal and witnessed overdoses

Concern has been expressed at the widespread prescribing of methadone in view of its inherent toxicity. Commentators have opined that methadone is more toxic than heroin and causes more overdose deaths. However, data deficiencies and flawed analyses leave continuing uncertainty about this crucial policy issue. The relative contributions of heroin, other opiates (e.g. methadone) and non-opiate drugs to overdose and overdose deaths among drug misusers were examined in a community-recruited sample of 312 injecting drug misusers in London. Data,were collected on last personal overdose (n = 117), last witnessed overdose (n = 167) and last,witnessed fatal overdose (n = 55), and on the different drugs that had been involved with these overdoses. Heroin was involved in 83% of last personal overdoses, 90% of last witnessed overdoses and 80% of last witnessed fatal overdoses, while other opiates were involved in only 18%, 8% and 26%, respectively. Methadone accounted for about half of these "other opiate" overdoses. Overdoses involving a combination of heroin and a non-opiate were common-29%, 21% and 39%, respectively. Heroin was the drug most frequently involved in overdose across all three areas of study. However, combinations of heroin and a non-opiate were surprisingly frequent, especially in witnessed fatal overdoses (as reported recently by other investigators using different methodologies). Considering the wide extent of methadone prescribing to this group, methadone was remarkably infrequently reported as responsible (solely or in combination) for either personal overdoses, witnessed overdoses or witnessed fatal overdoses.