The initiation of substance use is a key subject of investigation in prevention-related research, as the earliest indicators of potential substance-related problems manifest during this first stage of use. For both licit and illicit drugs, early age at first use is a marker of elevated risk for developing substance use disorders (SUDs). The relationship between early onset and later problem use has been demonstrated for alcohol (Chou and Pickering, 1992; Grant and Dawson, 1997; Hingson et al., 2006; McGue et al., 2001; Prescott and Kendler, 1999), cigarettes (Everett et al., 1999; Hu et al., 2006), and other drugs (Anthony and Petronis, 1995; Grant and Dawson, 1998; King and Chassin, 2007). Elevation in risk for SUDs among early users has also been found across substances (Early onset cigarette smoking, for example, has been tied to both alcohol and drug use disorders [Grant, 1998; Grucza and Bierut, 2006; Hanna and Grant, 1999]), suggesting that early initiation reflects more global risk of pathological outcomes.
