OBJECTIVES: We examined whether frequent drug use increases the likelihood of subsequent sexual or physical intimate partner violence (IPV) and whether IPV increases the likelihood of subsequent frequent drug use. METHODS: A random sample of 416 women on methadone was assessed at baseline (wave 1) and at 6 months (wave 2), and 12 months (wave 3) following the initial assessment. Propensity score matching and multiple logistic regression were employed. RESULTS: Women who reported frequent crack use at wave 2 were more likely than non-drug using women to report IPV at wave 3 (odds ratio [OR]=4.4; 95% confidence interval [CI]=2.1, 9.1; P<.01), and frequent marijuana users at wave 2 were more likely than non-drug users to report IPV at wave 3 (OR=4.5; 95% CI=2.4, 8.4; P<.01). In addition, women who reported IPV at wave 2 were more likely than women who did not report IPV to indicate frequent heroin use at wave 3 (OR=2.7; 95% CI=1.1, 6.5; P=.04). CONCLUSIONS: Our findings suggest that the relationship between frequent drug use and IPV is bidirectional and varies by type of drug.