BACKGROUND AND AIMS: The market for new psychoactive substances (NPS) is highly dynamic, with hundreds of substances emerging on the European drug market in the last decade. 3-methylmethcathinone (3-MMC), a synthetic cathinone and isomer of mephedrone (4-MMC), gained popularity in the Netherlands due to its psychostimulant effects and initial legal status. The present study aimed to systematically examine developments in the Dutch 3-MMC market between 2012 and 2024, based on the Drugs Information and Monitoring System (DIMS) data, to describe trends in pricing, sources of purchase, chemical composition, user-reported effects and demographic and contextual use patterns.

DESIGN AND SETTING: Observational study using drug checking data collected from 2012 to 2024 through DIMS, a national network of 33 drug checking services operating throughout the Netherlands.

CASES: In total, 3437 samples sold as 3-MMC were submitted to DIMS for analysis and were included in the study. Of these, 2627 samples were chemically analysed.

MEASUREMENTS: Number of samples sold as 3-MMC submitted for drug checking, price, source of purchase, drug composition, self-reported effects in relation to drug composition, and setting of use.

FINDINGS: The number of samples sold as 3-MMC submitted to DIMS each year increased from n = 1 in 2012 to n = 1853 in 2024. Following the scheduling of 3-MMC in 2021, median prices doubled (from €10 during the period 2019-2021 to €20 in 2022) and the reported source of purchase shifted towards dealer (from approximately 50% of samples before scheduling to more than 90% after scheduling). Chemical composition of the analysed samples changed significantly (Cramér's V = 0.49, P < 0.01). Since 2022, samples sold as 3-MMC increasingly contained a variety of substances. By 2024, only 10% of samples still contained 3-MMC, compared with 85% in 2021, whereas substitutes such as 2-methylmethcathinone (2-MMC) and 3-chloromethcathinone (3-CMC), as well as more potent compounds including di(methyl)pentylone (DMP) and N-ethylnorpentedrone (NEP) became more prevalent. Self-reported effects (noted for 376 samples) were qualitatively similar for samples containing 2-MMC and 3-CMC compared with 3-MMC, whereas DMP and NEP were associated with more severe adverse reactions (e.g. anxiety, paranoia, cardiovascular disturbances, insomnia). Patterns of use shifted towards festivals and parties (around 50% and 25%, respectively), while home use (15%) remained notable in 2024.

CONCLUSIONS: The Dutch 3-methylmethcathinone (3-MMC) market changed substantially following scheduling in 2021, with more samples sold as 3-MMC submitted for drug checking. By 2024, only 10% of submitted samples contained 3-MMC and structurally related substitutes with greater health risks were increasingly detected.