Daily heroin injection and psychiatric disorders: A cross-sectional survey among People Who Inject Drugs (PWID) in Haiphong, Vietnam

•Regular heroin injection could be protective for depression and psychotic symptoms.•Psychiatric burden of methamphetamine use is high.•PWID treated with methadone are less often depressed.•Regular polysubstance use is associated with higher rate of psychiatric disorders. Psychiatric comorbidities are frequent among people who inject drugs, they are associated with a poorer prognosis and need to be addressed. Their interaction with daily heroin injection requires clarification. A cross-sectional survey was conducted among PWID recruited in the city of Haiphong, Vietnam, by respondent-driven sampling. The inclusion criteria were age 18 or older and current injection drug use, verified by skin marks and positive urine tests for heroin or methamphetamine. Data on socio-demographic characteristics, drug use, sexual behaviour and access to treatment were collected using face-to-face questionnaires by trained interviewers. PWID were screened by trained psychiatrists for depression, psychotic disorder and suicidality, using the MINI questionnaire. 418 participants were included in the analyses. All were injected heroin users, 21 % were diagnosed with a current major depressive disorder, 15 % with a current psychotic disorder and 12 % presented a suicide risk. In the bivariate analyses, regular meth use, cannabis use and ketamine use were positively associated with presenting at least one psychiatric condition while daily heroin injection and being currently treated with methadone were negatively associated. In the multivariate model, poly-substance use was positively associated with depression (methamphetamine and drinking in addition to heroin) and psychotic disorder (methamphetamine and/or hazardous drinking in addition to heroin) while daily heroin injection and current methadone treatment were negatively and independently associated with depression and psychotic syndrome. Our survey confirms the burden of methamphetamine use and the protective effect of methadone but also a possible protective effect of daily heroin injection.