Number of sexual partners and associations with initiation and intensity of substance use.

We dissected associations between initiation and intensity of substance use and number of sexual partners using pooled data from high school seniors (weighted n = 13,580) who participated in the 1999-2007 Youth Risk Behavior Surveillance System (YRBS), a cross-sectional, nationally representative survey. In multinomial multivariable logistic regressions, number of sexual partners steadily increased as substance use intensified from never use to experimental/new user to heavy use across all substances for both male and females. Severity of substance use is more closely related to, and thus a better indicator of, higher number of sexual partners than age of substance use onset.