Drug users were younger than non-users at first vaginal sex (mean, 15.2-16.1 vs. 17.3-17.5) and were more likely to have engaged in risky sexual behaviors during the last year, including having had sex with a non-monogamous partner (odds ratios, 3.3-5.2 for men and 2.9-6.5 for women), while high on alcohol or drugs (10.1-18.0 and 8.1-24.2), or in exchange for money or drugs (2.7-2.8 and 2.3-9.2),