By The Laboratory and Scientific Services
United Nations Office on Drugs and Crime; 

The scientific evaluation of substances for inclusion in international and most national legislations requires an assessment of a range of chemical, pharmacological, and toxicological properties of a substance. Also, for many of the NPS that have emerged, quality comparable scientific data on these properties are either scarce or do not exist. The aim of these UNODC guidelines is to support Member States in the generation of quality scientific data on key pharmacological properties used in the scientific evaluation of substances, specifically the determination of the abuse and dependence potential of NPS. Given the continued emergence of highly potent synthetic opioids in recent years, this guideline will focus on synthetic opioids and future volumes will contain information on other groups of NPS.

Vienna: UNODC< 2025. 58p.

By Luca Giommoni, Kirsty Stuart Jepsen, Shannon Murray

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.

Drug and Alcohol Dependence; 2025 Volume 276, 1 November 2025, 112900