Addiction vulnerability is an individual's risk of developing an addiction during their lifetime. There are a range of genetic and environmental risk factors for developing an addiction that vary across the population. Genetic and environmental risk factors each account for roughly half of an individual's risk for developing an addiction; the contribution from epigenetic (inheritable traits) risk factors to the total risk is unknown. Even in individuals with a relatively low genetic risk, exposure to sufficiently high doses of an addictive drug for a long period of time (e.g., weeks–months) can result in an addiction. In other words, anyone can become an individual with a substance use disorder under particular circumstances. Research is working toward establishing a comprehensive picture of the neurobiology of addiction vulnerability, including all factors at work in propensity for addiction.
Three-factor model
Accepted research now shows that some people have vulnerabilities to addiction and has established a three-factor standard for vulnerability to drug addiction: genetic factors, environmental factors, and repeated exposure to drugs of use. Being vulnerable to addiction means there is a factor that makes one individual more likely to develop an addiction than another individual. Additionally, many in the science community agree that addiction is not simply just a result of desensitized neural receptors but also a corollary of long-term associated memories (or cues) of substance use and self-administration. Vulnerability to addiction has both physiological and biological components.
Genetic factors
Contemporary research in neurobiology (a branch of science that deals with the anatomy, physiology, and pathology of nervous system) 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. 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, but also compensated levels of the cannabinoid receptor type CB1.
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. This naturally occurring deficiency is one of the most studied genetic vulnerabilities to substance abuse across the field. Recent studies show that GABA also plays a role in vulnerability to addiction. When alcohol is consumed it affects GABA by mimicking its effects on the brain, such as basic motor functions.
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.
Environmental factors
A major environmental factor that increases vulnerability to developing addiction is availability of drugs. Additionally, socioeconomic status and poor familial relationships have been shown to be contributing factors in the initiation and continued use of alcohol or other drugs. Neurobiology plays a role in addiction vulnerability when in combination with environmental factors. Chronic stressors contribute to vulnerability because they can put the brain in a compromised state. External stressors (such as financial concerns and family problems) can, after repeated exposure, affect the physiology of the brain.