Substance use and psychiatric outcomes following substance use disorder treatment: An 18-month prospective cohort study in Chile.

Background And Aims: Evidence from high-income countries has linked duration and compliance with treatment for substance use disorders (SUDs) with reductions in substance use and improvements in mental health. Generalizing these findings to other regions like South America, where opioid and injection drug use is uncommon, is not straightforward. We examined if length of time in treatment and compliance with treatment reduced subsequent substance use and presence of psychiatric comorbidities.

Design: Prospective cohort analysis (3 assessments, 18 months) using inverse probability weighting to account for confounding and loss to follow-up.

Settings: Outpatient/inpatient programs in Región Metropolitana, Chile.

Participants: Individuals initiating publicly funded treatment (n = 399).

Measurements: Exposures included length of time in (0-3, 4-7, 8 + months, currently in) and compliance with treatment (not completed, completed, currently in) measured in the intermediate assessment (12 months). Primary outcomes were past-month use of primary substance (most problematic) and current psychiatric comorbidities (major depressive episode, panic, anxiety or post-traumatic stress disorders) measured 6 months later (18 months). Secondary outcomes included past month use of alcohol, cannabis, cocaine powder and cocaine paste.

Findings: 18.3% [95% confidence interval (CI) = 14.7%-22.6%] of individuals participated for 3 or fewer months in treatment and 50.1% (95% CI = 45.2%-55.1%) did not complete their treatment plan at 12 months. Participating for 8 + months in treatment was associated with lower risk of past month use of primary substance at 18 months [vs. 0-3 months, risk ratio (RR) = 0.62, 95% CI = 0.38-1.00] and completion of treatment (vs. not completed, RR = 0.49, 95% CI = 0.30-0.80). Neither participating 8 + months (vs. 0-3 months, RR = 0.83, 95% CI = 0.57-1.22) nor treatment completion (vs. not completed, RR = 1.02, 95% CI = 0.72-1.46) were associated with lower risk of psychiatric comorbidity at 18 months.

Conclusions: Longer time in treatment and compliance with treatment for substance use disorders in Chile appears to be associated with lower risk of substance use but not current comorbid psychiatric conditions 18 months after treatment initiation.