ObjectivesMen who have sex with men (MSM) are at increased risk for STIs and mental disorders. Syndemic theory holds that psychosocial issues co-occur and interact, and thus increase sexual risk behaviour. Psychosocial issue identification, referral and management might reduce risk behaviour.MethodsIn the syndemic-based intervention study, an open-label randomised controlled trial, MSM were enrolled at the STI outpatient clinic of the Public Health Service of Amsterdam. We screened participants using validated questionnaires on the following problem domains: alcohol and substance use, sexual compulsivity, anxiety, depression, attention deficit hyperactivity disorder, alexithymia, intimate partner violence and childhood sexual abuse. Individuals were randomly assigned (1:1) to receive either tailored, face-to-face feedback and help-seeking advice on mental health screening, or no feedback and no help-seeking advice. Participants were followed trimonthly for a year. The primary outcomes were self-reported and confirmed help-seeking behaviour.ResultsWe included 155 MSM: 76 in the intervention group and 79 in the control group. At inclusion, 128 participants (83.1%) scored positive in at least one problem domain. We found no significant differences in self-reported or confirmed help-seeking behaviour between the intervention and the control group: 41% vs 29% (p=0.14) and 28% vs 22% (p=0.44), respectively. There were also no differences in STI incidence and condomless anal sex acts between the two groups.ConclusionScreening showed high prevalence of problems related to mental health and substance use, while tailored feedback, advice and referral did not significantly increase help-seeking behaviour. Other interventions are needed to tackle the high burden of mental disorders among MSM.Trial registration numberNCT02859935.