BackgroundSuboptimal adherence to tuberculosis (TB) treatment is associated with increased disease recurrence and death. Little research has been conducted in India to understand TB medication non-adherence.MethodsWe enrolled adult drug-susceptible TB patients, about half of whom were people living with HIV (PLHIV), in Chennai, Vellore, and Mumbai. We conducted a single unannounced home visit to administer a survey assessing reasons for non-adherence and collect a urine sample that was tested for isoniazid content. We described patient-reported reasons for non-adherence and identified factors associated with non-adherence (negative urine test) using multivariable logistic regression. We also assessed the association between non-adherence and unfavorable treatment outcomes.ResultsOf 650 patients in the cohort, 77 (11.8%) had a negative urine test result. Non-adherence was independently associated with daily wage labor (aOR 3.1, CI: 1.3—7.7), smear-positive pulmonary disease (aOR 2.1, CI: 1.1—4.1), alcohol use (aOR 2.3, CI: 1.1—4.8), and spending 60 minutes or more picking up medication refills (aOR 9.1, CI: 1.8—45.4). PLHIV reported greater barriers to picking up medications than non-PLHIV. Among 167 patients who reported missing doses, common reasons reported included traveling away from home, forgetting, feeling depressed, and running out of pills. The odds of non-adherence was 3.8 (CI: 2.1—6.9) times higher among patients with unfavorable treatment outcomes compared to those with favorable outcomes.ConclusionAddressing structural and psychosocial barriers will be critical to improve TB treatment adherence in India. Urine isoniazid testing may help identify non-adherent patients to facilitate early intervention during treatment.Key pointsWe evaluated adherence to tuberculosis medications in 650 Indian patients by conducting urine isoniazid tests collected during unannounced home visits. Structural barriers to collecting medication refills and psychosocial barriers emerged as the most important factors contributing to medication non-adherence.