Contemporary research in the neurobiology of addiction points to genetics as a major contributing factor to addiction vulnerability. It has been estimated that 40-60% of the vulnerability to developing an addiction is due to genetics.[5][6] One gene in particular, the D2 subtype of dopamine receptor has been studied at length in association to substance addiction. The D2 receptor responds to the chemical dopamine which produces rewarding and pleasurable feelings in the brain. Through mice studies, agreeing contemporary research has shown that individuals with a deficiency in this dopamine receptor exhibit not only a preference for and increased consumption of alcohol over their genetically normal peers,[7] but also compensated levels of the cannabinoid receptor type CB1.[7] This suggests that both of these genetic factors work together in the regulation of alcohol and cocaine in the brain and in the normal regulation of dopamine. Individuals with this genetic deficiency in the D2 dopamine receptor may be more likely to seek out these recreational pleasure/reward producing substances as they are less receptive to the natural “feel good’’ effects of dopamine.[7] This naturally occurring deficiency is one of the most studied genetic vulnerabilities to substance abuse across the field.

Additionally, genetics play a role on individual traits, which may put one at increased risk for experimentation with drugs, continued use of drugs, addictions, and potential for relapse. Some of these individual personality traits, such as impulsivity, reward-seeking, and response to stress, may lead to increased vulnerability to addiction.[8]

https://en.wikipedia.org/wiki/Addiction_vulnerability#Genetic_Factors Follow links for specifics