An index of fatal toxicity for new psychoactive substances.

An index of fatal toxicity for new psychoactive substances has been developed based solely on information provided on death certificates. An updated index of fatal toxicity (Tf), as first described in 2010, was calculated based on the ratio of deaths to prevalence and seizures for the original five substances (amphetamine, cannabis, cocaine/crack, heroin and 3,4-methylenedioxymethylamphetamine)*. These correlated well with the 2010 index. Deaths were then examined for cases both where the substance was and was not found in association with other substances. This ratio (sole to all mentions; S/A) was then calculated for deaths in the period 1993 to 2016. This new measure of fatal toxicity, expressed by S/A, was well-correlated with the index Ln (Tf) of the original reference compounds. The calculation of S/A was then extended to a group of new psychoactive substances where insufficient prevalence or seizure data were available to directly determine a value of Tf by interpolation of a graph of Tf versus S/A. Benzodiazepine analogues had particularly low values of S/A and hence Tf. By contrast, γ-hydroxybutyrate/γ-butyrolactone, α-methyltryptamine, synthetic cannabinoid receptor agonists and benzofurans had a higher fatal toxicity.