Factors that contribute to the development of heroin addiction, besides the drug of abuse itself, are both genetic and environmental. Epidemiological studies indicate that genetic factors, both those shared by addiction to several drugs of abuse and those specific for addiction to a given drug, contribute approximately 40-60% of the risk of developing heroin addiction (Kendler et al., 2003, Tsuang et al., 1998, Tsuang et al., 1996). One study found 38% genetic variance specific to the development of heroin addiction, a variance higher than that for marijuana, stimulants, sedatives, or psychedelics (Tsuang et al., 1998). Genetic predisposition may explain why approximately one-third of those self-exposed to opiates become addicted (Kreek, 2002).
