Objectives .In Ethiopia, little is known about the association between substance use disorders and adherence to antituberculosis (anti-TB) medications. Therefore, the objective of this study was to assess the effect of substance use disorders on adherence to anti-TB medications in Southwest Ethiopia.

Design. Prospective cohort study.

Settings. Patients were recruited from 22 health centres and four hospitals in Southwest Ethiopia.

Participants. This study was conducted among 268 patients with TB, aged 18–80 in Southwest Ethiopia between October 2017 and October 2018. At baseline, patients who were exposed substance use disorders (134 patients) and unexposed to substance use disorders (134 patients) were recruited. Patients were followed for 6 months, and data were collected on three occasions.

Main outcome measure. Adherence to anti-TB medications.

Results. Patients with substance use disorders had consistently higher prevalence of non-adherence than those without, 16.4% versus 3.0% at baseline, 41.7% versus 14.4% at 2-month follow-up and 45.7% versus 10.8% at 6-month follow-up assessments. Patients with khat use disorder were 3.8 times more likely to be non-adherent to anti-TB medications than patients without khat use disorder (Adjusted odds ratio (aOR)=3.8, 95% CI 1.8 to 8.0). Patients who had alcohol use disorder (AUD) were also 3.2 times likely to have poor adherence compared with their counterparts (aOR=3.2, 95% CI 1.6 to 6.6). In addition, being educated (aOR=4.4, 95% CI 1.7 to 11.3), and being merchant (aOR=6.1, 95% CI 1.2 to 30.8) were associated with non-adherence to anti-TB medications.

Conclusion. Khat and AUDs predict greater likelihood of non-adherence to anti-TB medication. This implies the need to integrate the management for substance use disorders into the existing TB treatment services.