It should be noted that the associations between the ages of substance use initiation and symptoms of substance use disorder were modest (men: rs=−0.10 – −0.31, women: rs=−0.12 – −0.28). Thus, addressing shared mechanisms of liability for early initiation and disorder and delaying the timing of first use will likely reduce only a small amount of the risk for substance use problems. This is not unexpected, however, given that substance use disorders have been associated with a number of biological and psychosocial factors, many of which may confer only a small degree of liability. To generate a more complete profile of risk for substance-related problems, the present findings should be integrated with those from genetically-informed studies of additional risk factors and associated behaviors.
