Dozens of studies have demonstrated links between genetics, various environmental factors, and a person’s susceptibility to addiction. Many of these studies focus on alcoholism (addiction to alcohol), but others have extended the findings to other addictions.
Numerous genetic variations can directly impact the risk for alcoholism, usually by altering the ways in which alcohol is experienced and processed in the body and brain. In one study, scientists found that people who naturally have less reactivity to alcohol (as measured by body sway) are more likely to become alcoholic. Basically, the study found that people who are genetically less susceptible to the unpleasant side effects of alcohol (falling down, getting sick, passing out, etc.) are more likely to drink alcoholically. Another study links a specific genetic variation affecting D2 dopamine receptors, which are part of the “reward center” in the brain, to addiction. This genetic mutation, which essentially magnifies the pleasurable effects of addictive substances and behaviors, increases the risk for not just alcoholism but other types of addiction.
Genetic variations can also reduce the risk for alcoholism. For example, it has long been known that people of East Asian ancestry are less likely than other groups to become alcoholic. And scientists now know why. Research has identified a genetic variation prevalent in East Asian cultures that causes a deficiency of an enzyme (aldehyde dehydrogenase) that is critical to the metabolism of alcohol. When alcohol is consumed by people with this genetic variation, classic hangover symptoms—headache, dehydration, nerve and tissue sensitivity, rapid heartbeat, nausea, and the like—occur almost immediately. Alcohol makes these individuals physically ill instead of getting them high. Unsurprisingly, alcoholism is incredibly rare among people with this genetic makeup.
Genetics can also indirectly impact the risk for addiction. For instance, genetics are a factor with numerous psychological disorders like depression, anxiety, ADHD, OCD, bipolar disorder, schizophrenia, etc. And guess what? Many of the people struggling with these disorders choose to self-medicate with alcohol, drugs, or potentially addictive behaviors. Over time, this can become a go-to coping mechanism that eventually turns into an addiction. In such cases, what is genetically inherited is not a unique response to a specific substance or set of behaviors, but the propensity for an underlying neurobiological vulnerability that can, over time, lead to an addiction.
Research tells us that we can’t blame addiction entirely on genetic susceptibility; environmental factors also play a significant role. But how big a role is this, and how can we measure it? One way is to study the incidence of addiction among adopted children and twins (especially identical twins who were separated at birth and raised by different sets of parents). In this way, the relative influence of genetic risk factors versus environmental risk factors can be measured.
Adoption studies typically ask: What happens to the biological children of addicts if they’re adopted into a family where neither parent is addicted? Research has consistently found that people with biological but not adoptive parents who were addicts are more likely to develop an addiction. So score a point for genetics. That said, being more likely to develop an addiction doesn’t mean that addiction is an absolute certainty. In fact, lots of people in these studies did not become addicted. Plus, there are plenty of biological children of non-addicts who become addicts. So now we can score a few points for nurture.
Twin studies are even more enlightening. First of all, there are two types of twins: dizygotic (fraternal) twins, who have half their genes in common, and monozygotic (identical) twins, who carry exactly the same genes. Studies consistently show that siblings in both twin types show a common risk toward addiction. If one twin is addicted, there is an increased likelihood that the other is also addicted. Predictably, the correlation is higher for identical twins than it is for fraternal twins. However, the numbers do not exactly match up, and there are plenty of instances where one twin is alcoholic and the other is not. And this is true regardless of whether they are fraternal or identical, and regardless of whether they were raised together or separately. So it’s clear that genetic predisposition toward addiction is not an automatic life sentence; environment also plays a part.
- 1.8 times as likely to smoke cigarettes
- 1.9 times as likely to become obese
- 2.4 times as likely to experience ongoing anxiety
- 3.6 times as likely to be depressed
- 3.6 times as likely to qualify as promiscuous
- 7.2 times as likely to become alcoholic
- 11.1 times as likely to become an intravenous drug user.
Thus, there is an undeniable link between early-life trauma and adult-life symptoms and disorders, especially addiction.
Addiction Risk: A Mix of Factors
Based upon considerable amounts of research, it is clear that addiction arises based on a number of risk factors. Moreover, those risk factors tend to intertwine and build upon one another. So it appears that, at the end of the day, the conversation about the cause of a person’s addiction is less about nature vs. nurture and more about how various risk factors, both nature and nurture, come together to influence that individual’s thinking and behaviors.