Aims: This study investigated patterns and trajectories of substance use, with a special focus on illicit drugs other than cannabis. It examined both patterns and trajectories of use among a general population-based sample. Methods: We used data from the 2011 French ESCAPAD survey of French 17-year-olds to assess exposure and age of initiation of 14 licit and illicit drugs (N=23,882). Latent class analysis (LCA) and survival analyses were performed. Results: The results of the LCA showed that

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... tterns of illicit drug use clearly distinguished between two groups of other illicit drugs: 1) amphetamines/speed, cocaine, ecstasy/MDMA, magic mushrooms, poppers, and solvents; 2) crack/freebase, GHB/GBL, heroine, LSD, and ketamine. Survival analyses highlighted that trajectories involved the first group before the second one. Conclusions: Prototypical drug use patterns and trajectories should include a distinction between two groups of illicit drugs. Preventive actions should focus on young people in their early teens, since very young users are more likely to progress to illicit drug use, and further studies should include this distinction instead of aggregating other illicit drugs into a single category. Keywords General population-based sample, patterns of drug use, stages of drug use History