Background: Men present higher overall rates of substance use and abuse than women; yet, evidence suggests that an increase of substance use by the younger cohorts of women in recent decades is narrowing this gap in western societies. Moreover, younger cohorts may also be reporting earlier initiation of substance use, representing an increased risk for developing substance-related problems. With this study we intend to identify changes in the patterns of substance use of men and women in Spain for public health policy, planning and intervention.

Methods: Sex differences in the cumulative incidence of alcohol, tobacco, cannabis and cocaine were examined by birth cohort using a combined sample of individuals aged 15-64 years from eight editions of the Spanish National Survey on Drugs (1995-2009).

Results: Initiation of substance use in Spain is progressively taking place at younger ages, particularly among women. The gender-gap of life-time occurrence of substance use is narrowing (cannabis and cocaine) almost closing (alcohol) and even reversing (tobacco) in the youngest cohort.

Conclusion: These results reflect the particular evolution and trends of Spanish society regarding substance use. Women's increased use of substances and the earlier age of initiation of substance use by both sexes present particular challenges for prevention and treatment of future substance-related problems. The trends registered for legal and illegal substances would require re-evaluation of existing prevention policies.