BACKGROUND AND AIMS: Use of the synthetic methylmethcathinones 2-MMC and 3-MMC (2/3-MMC) is emerging, especially among young people, but their health risks remain unclear.

METHOD: A systematic narrative review was conducted on studies describing the availability, pharmaco-toxicological profile, and user characteristics of 2/3-MMC, with a focus on the situation in The Netherlands.

RESULTS: Among nightlife youth (16-35 yrs.) in The Netherlands, reported past-year 3-MMC use increased almost four-fold within two years,and in 2022 became the third most commonly used substance (33.7 %), after cannabis and MDMA. 2/3-MMC appears to have a pharmaco-toxicological profile similar to 4-MMC (mephedrone), with similar dopaminergic but less serotonergic activity. Their shorter duration of action may lead to increased craving and more frequent re-dosing compared to 4-MMC. Low price, high availability and positive recommendations on social media have attracted (very) young (aged 14-17), who are often particularly vulnerable. Despite a legal ban on 3-MMC in 2021, the number of individuals seeking treatment for problematic 3-MMC use in the Netherlands rose from 33 in 2021 to 330 in 2023. Most cases involved polydrug users.

CONCLUSIONS: In general, 2/3-MMC appear to be less toxic and harmful than other illicit substances though their use may result in more craving, more frequent re-dosing and, thus, to more dependence than 4-MMC. The number of treatment seeking problematic 3-MMC users is increasing. Drug regulation may help prevent a further rise in 2/3-MMC use, although a shift to other cathinones cannot be ruled out. Mental health organisations should therefore remain vigilant to monitor problematic 2/3-MMC use, especially among vulnerable (very) young users.