Association between ABCB1 C3435T polymorphism and increased risk of cannabis dependence. (2009).  Patients with cannabis dependence (n=40) had a significantly higher 3435C allele frequency (62.5% versus 43.8% respectively, P=0.017) and CC genotype (50% versus 20%, P=0.005, OR=4.00 [1.50-10.60]). The CC genotype was independently associated with cannabis dependence. This is the first time a significant specific genetic marker has been shown in cannabis dependence. ABCB1 polymorphisms may alter Delta9THC distribution, its psychoactive effects and individual vulnerability to dependence.