BACKGROUND: 'Chemsex' is the use of drugs before or during planned sexual events to facilitate, enhance, prolong and sustain the experience. Drugs associated with chemsex are methamphetamine, GHB/GBL, mephedrone, cocaine and ketamine. This review syntheses published research on the antecedents, behaviours and consequences associated with chemsex behaviours among men who have sex with men (MSM). METHODS: Papers from high income countries which were published between January 2000 and September 2018 reporting the use of chemsex drugs before or during sex were identified through Medline, Web of Science, CINAHL and Central. Results were synthesised using a narrative approach and conceptualised using a behavioural analysis framework. RESULTS: The search identified 2492 publications, of which 38 were included in the final synthesis. There were wide variations in chemsex prevalence estimates due to the heterogeneous sampling in the studies. Chemsex participants have expectations that the drugs will positively affect their sexual encounters and HIV positive MSM are more likely to engage in the behaviour than HIV negative MSM. There were wide ranging prevalence estimates on injecting drugs for sexual purposes and the sharing of injecting equipment with some evidence of unsafe injecting practices. Participants were more likely to engage in condomless anal intercourse than men who do not engage in chemsex. This may increase the risk of transmission for HIV and other sexually transmitted infections. CONCLUSION: A minority of MSM appear to engage in chemsex behaviours but they are at risk of this negatively impacting on their health and well-being. Further research is required to examine high risk chemsex behaviours, impact of chemsex on psycho-social well-being and if chemsex influences uptake of PrEP, PEP and sexual health screening.