786 JOURNAL OF STUDIES ON ALCOHOL AND DRUGS / SEPTEMBER 2009 Smoking and Illicit Drug Use Associations With Early Versus Delayed Reproduction: Findings in a Young Adult Cohort of Australian Twins*

ABSTRACT. Objective: This article examines relationships between reproductive onset and lifetime history of smoking, regular smok-ing, and nicotine dependence, and cannabis and other illicit drug use. Method: Data were drawn from a young adult cohort of 3,386 female and 2,751 male Australian twins born between 1964 and 1971. Survival analyses were conducted using Cox proportional hazards regression models predicting age at fi rst childbirth from history of substance use or disorder separately by substance class. Other substance use or disorder, including alcohol dependence, as well as sociodemographic characteristics, history of psychopathology, and family and childhood risks, were included as control variables in adjusted models. Results: Regular smoking and nicotine dependence were associated with earlier reproduction, with pronounced effects for women. For women, use of cannabis was associated with early reproduction before age 20, and with delayed reproduction among women who have not reproduced by age 2