Mexico's precursor chemical controls: emergence of less potent types of methamphetamine in the United States.

Background: This study examines whether Mexico's controls on ephedrine and pseudoephedrine, the two precursor chemicals that yield the most potent form of methamphetamine, d-methamphetamine, impacted the prevalence/availability of less potent types of methamphetamine in the United States-types associated with the alternative precursor chemical P2P.

Method: Using ARIMA-intervention time series analysis of monthly drug exhibits (a prevalence/availability indicator) from the System to Retrieve Information from Drug Evidence (STRIDE), we tested whether Mexico's controls, which began in 2005, were associated with growth/decline in d-methamphetamine and growth/decline in P2P-associated, less potent l-methamphetamine, racemic methamphetamine (a 50:50 ratio of d- and l-isomers), and mixed isomer methamphetamine (an unequal ratio of d- and l-isomers). Heroin, cocaine and marijuana exhibits were used for quasi-control (01/2000-04/2011).

Results: Mixed-isomer exhibits constituted about 4% of the methamphetamine exhibits before Mexico's controls, then rose sharply in association with them and remained elevated, constituting about 37% of methamphetamine exhibits in 2010. d-Methamphetamine exhibits dropped sharply; l-methamphetamine and racemic methamphetamine exhibits had small rises. d-Methamphetamine exhibits partially recovered in the US West, but little recovery occurred in the US Central/South. Quasi-control series were generally unaffected.

Conclusion: The US methamphetamine market changed. Widespread emergence of less potent methamphetamine occurred in conjunction with Mexico's controls. And prevalence/availability of the most potent type of the drug, d-methamphetamine, declined, a partial recovery in the West notwithstanding. Granting that lower potency drugs typically engender less dependence and attendant problems, these findings suggest that, following Mexico's controls, the potential harm of a sizeable amount of the US methamphetamine supply decreased.