Epidemiologic and preclinical data suggest that the use of marijuana in adolescence could influence multiple addictive behaviors in adulthood. In rodents exposed to cannabinoids during adolescence, there is decreased reactivity of the dopamine neurons that modulate the brain’s reward regions.18 The exposure of rodents to cannabis in utero alters the developmental regulation of the mesolimbic dopamine system of affected offspring.19 If reduced dopamine reactivity in the brain’s reward regions does follow early exposure to marijuana, this effect could help to explain the increased susceptibility to drug abuse and addiction to several drugs later in life, which has been reported in most epidemiologic studies.20 This theory is also consistent with animal models showing that THC can prime the brain for enhanced responses to other drugs.21 Although these findings support the idea that marijuana is a gateway drug, other drugs, such as alcohol and nicotine, can also be categorized as gateway drugs, since they also prime the brain for a heightened response to other drugs.22 However, an alternative explanation is that people who are more susceptible to drug-taking behavior are simply more
