BACKGROUND:
Substance use is associated with HIV sexual risk behaviors, yet few studies have examined substance use patterns longitudinally. We evaluated the types and frequency of substances used over a six-month period among U.S. women at risk for HIV acquisition.

METHODS:
Women reporting unprotected sex with a man in the previous six months and at least one other personal or partner HIV risk characteristic enrolled in a multisite cohort study and completed interviews about substance use at study visits. Prevalence and frequency of substance use at the baseline and six-month visits were compared and correlates of decreased substance use at the six-month visit were assessed.

RESULTS:
Of 2099 women enrolled, 1882 had substance use data at baseline and six-months. Of these, 76.1% reported using at least one drug or binge drinking in the previous six months; 37.5% were frequent and 38.6% non-frequent substance users. Binge drinking was most frequently reported (63.3%), followed by cocaine (25.0%) and opioids (16.5%). Fifty-five percent of opiate users and 30% of cocaine users reported daily/almost daily use. At the six-month visit, 40.5% reported a decrease in frequency of use. Adjusting for income and type of drug used, poly-substance users were less likely to decrease frequency of use compared to those who only used one substance.

CONCLUSION:
A substantial decrease in frequency of substance use over time was observed in this cohort. Poly-substance users were less likely to reduce frequency of use over time, suggesting that specific substance use interventions targeting these users are warranted.