A behavioural economic analysis of alcohol, amphetamine, cocaine and ecstasy purchases by polysubstance misusers

Behavioural economic models of substance choice describe the relationship between changes in unit price and consumption. As the majority of UK non-dependent substance misusers are polysubstance misusers, we investigated the influence of price upon hypothetical purchases of alcohol, amphetamine, cocaine and ecstasy. Forty-three current polysubstance misusers (25 males, 18 females; mean age 21.3 +/- 2.8) were recruited into the study. As the price of alcohol rose, demand was inelastic. Amphetamine was a substitute for alcohol, cocaine was a compliment drug and ecstasy was independent. Demand for amphetamine was elastic as its price rose, but only alcohol was identified as a substitute drug and other drug purchases were independent of amphetamine price. As the price of cocaine increased, demand was elastic. Alcohol and ecstasy were substitute drugs but amphetamine purchase was independent, indicating asymmetrical substitution of alcohol and cocaine. Finally, demand for ecstasy was also elastic, but only cocaine substituted as ecstasy price rose. These results extend previous findings in substance dependent populations using behavioural economic models and support the opinion that purchasing substances is a complex process, involving both socio-economic and psychopharmacological factors. Whilst subjects expressed a preference for ecstasy, these behavioural findings indicated that alcohol was their drug of choice when economic considerations were brought into play. Self-reported drug preference, although facilitating between subjects experimental design, may therefore not accurately represent real world polysubstance misuse.