“Chemsex” means sex, generally between men, occurring under the influence of drugs taken immediately before and/or during the sexual session. “Slam” is defined by injection of psychostimulant drugs in the same context. The Parisian Addictovigilance Center presents preliminary results of a specific harm reduction program for slammers and chemsexers, based on the analysis of new psychoactive substances (NPS). Study was built by stages: (1) questionnaire of evaluation on chemsex practice, (2) toxicological analysis of collected drugs samples, (3) communication of results during Focus Groups with impact assessment. From January to September 2016, 17 questionnaires on chemsex practice and 31 samples were collected. Fifteen participants out of 17 were slammers. Motivations were mainly disinhibition and seeking pleasure (14 mentions) or prolonging pleasure (11 mentions). Collected samples were presented as cathinones (alpha-PVP, 4F-PVP, PVP-8, 3-MMC, 2-MMC, 4-MEC, methylone, MDPV), other phenethylamines (2-FMA, methamphetamine, 3,4-CTMP, 3-FPM) and cocaine. Analytical results show a 90% adequacy between the announced substance and the identified molecule. The Focus Group revealed a final level of knowledge on the harm reduction questionnaire at 9.4 on a scale of 12 items with a positive impact on: opinion on sample analysis (+1 point at the end of the session) and knowledge of the products (+0.6 points). This study is still ongoing and the final results should allow the implementation in routine practice of a validated approach of harm reduction in this specific population.