Does Regulating Drug Precursors Affect Illicit Drug Markets? An Expanded and Updated Systematic Review

Background Many countries are placing greater emphasis on regulating precursor chemicals used in illicit drug production. However, the latest review on this topic is 14 years old and limited to North American methamphetamine regulations. This review updates and expands on past work by assessing how precursor regulations affect illicit drug markets. Method We conducted a systematic review following PRISMA guidelines, searching 13 databases and relevant organizational websites for grey literature. Eligible studies quantitatively assessed precursor regulations' impact on drug supply, demand, or related harms. Due to intervention variability, we used narrative synthesis. Bias risk was evaluated with the EPOC Risk of Bias Tool. Results Twenty-six studies met the inclusion criteria, published between 2003 and 2023, focusing on methamphetamine (n=23), cocaine (n=3), and heroin (n=1). Most were from the USA (n=20), with others from Canada (n=1), Mexico (n=1), Australia (n=3), and the Czech Republic (n=1). The studies assessed 12 outcomes across 37 interventions, 14 of which were effective and 23 ineffective. Effective interventions led to impacts such as a 100% price increase, a 40% purity reduction, and a 43% drop in past-month drug use, lasting from months to seven years. Ineffective interventions shared three issues: targeting unused chemicals, focusing on small-scale operations, or failing as suppliers adapted to new sources or routes. Conclusions Precursor regulations can reduce the supply, use, and harms of heroin, cocaine, and methamphetamine. However, they are not a one-size-fits-all solution. Their effectiveness depends on how they are designed and the context in which they are implemented.