Drug content of powders and other illicit preparations in the UK

Information on the purity of illegal drugs is used for various purposes including: valuation for sentencing; profiling and sample comparison; and studies of the economics of the illicit market. The most commonly-used measure for powders is the arithmetic mean purity, but this statistic has several drawbacks. In the case of amphetamine, the mean (10% in 1995) has been consistently higher than the mode (4% in 1995), and it is a function of seizure size, region and time. Heroin purity, as measured by the diamorphine content (mean=42% in 1995) could also be an unreliable guide to potency if other opium alkaloids and 'active' adulterants are present. The mean purities of cocaine and crack in 1995 were 51% and 85%, respectively. A further source of confusion can arise when a distinction is not made with respect to the chemical form of the drug (i.e. salt or base). (C) 1997 Elsevier Science Ireland Ltd.