The Science Behind Drug Addiction: More Than Just Chemical Hooks, The Harvard Brain, Volume 5, Issue 1

Drug addiction is arguably one of the most stigmatized topics in society; mentioning it may conjure images of individuals in desperate need of their next “fix.”  Few look upon drug addicts positively, viewing them as “selfish” or “criminal” individuals who are undeserving of empathy (Bustos-Gamiño et al., 2022). In fact, people are more likely to harbor negative attitudes toward those suffering from substance use disorder (SUD) than those with mental illness (Barry et al., 2014). Moreover, there is skepticism regarding the effectiveness of interventions for drug addiction, coupled with discrimination against policies aimed at aiding those affected, including those related to housing and insurance.

Undoubtedly, substance addiction entails distinct chemical interactions. Alcohol interferes with neuronal communication, disrupting neurotransmitter systems by upsetting the balance between the inhibitory and excitatory components—contributing to the neurological conditions associated with drunkenness, such as drowsiness, lowered inhibitions, and impaired decision-making. Heroin converts to morphine once it enters the brain, binding readily to endogenous opioid receptors and stimulating excessive dopamine release. Opioids such as heroin or fentanyl are extremely addictive in large part due to this mechanism—the delivery of such an intense euphoric high eventually creates an increased tolerance with repeated usage. This subsequently leads to a chemical dependence of the brain on opioids, which can produce damaging withdrawal effects if the person were to stop using the drug. 

This information is widely recognized, as it is typically included in the curriculum of almost every education system, addressing the chemical "hooks" of drug addiction. However, while chemical biology is the physical mechanism by which addiction occurs, it does not fully explain the underlying factors behind addiction susceptibility. A person’s environment undoubtedly plays a role in the development of addictive behavior. If one grows up around parents or peers who regularly use drugs, they are more likely to engage in substance use that could lead to addiction (Mennis et al., 2016). As such, the immersion of children and adolescents in these environments can easily motivate emulated behavior later in their own lives.  

However, research efforts have also demonstrated the heritability of SUDs, with current research identifying specific genes complicit in predisposition to drug addiction (Ducci & Goldman, 2012). Perhaps there is some subconscious understanding that people possess intrinsic qualities that factor into their susceptibility to developing a SUD. However, many people ascribe these qualities to a person’s character, leading to a stigmatized view of the morality of drug addicts.

While it is true that risky environments spur drug addiction, there is a similarly crucial environmental component in the form of social relationships. For instance, relationship stress and jealousy can lead to increased drinking frequency and risk of alcohol abuse. In contrast, healthy, reciprocal relationships were also demonstrated to play a significant role in the potential reduction of or abstention from substance use (Rodriguez & Derrick, 2017). In particular, among newlywed couples in which at least one partner smokes, those with high perceived responsiveness from one another showed decreases in the use of cigarettes and the likelihood of continued smoking over the following nine years. Many partners were also motivated to quit smoking by the fear of harming their partner. As such, interventions for smoking were more successful when presented in light of couple-based outcomes as compared to individual-based outcomes. 

Additionally, many studies involving mice have demonstrated the causal relationship between social isolation and substance use. In adolescent mice, for instance, early social isolation resulted in increased seeking and motivation for heroin (Singh et al., 2022). Other studies have similarly shown that disrupted social development, especially in the form of early social experiences during the post-weaning phase, causes long-lasting increases in the motivation to self-administer cocaine (Baarendse et al., 2013). This increase is specific to drug reward and not a dopamine release in general, as social isolation did not impact sucrose self-administration nor motivation for sucrose (Fosnocht et al., 2018). Oxytocin, a neurotransmitter colloquially known as the “love hormone,” can be triggered by soothing social behaviors such as affectionate touch. It has been shown that the injection of oxytocin into the nucleus accumbens (a region of the brain primarily related to the modulation of pleasure, reward, and addiction) of rats demonstrated a reduction in methamphetamine-induced reward and decreased relapse to meth-seeking behavior (Baracz et al., 2014). 

Although these experimental studies are difficult to replicate in human subjects, since it is ethically objectionable to subject humans to social isolation with the aim of inducing drug addiction, there have been studies demonstrating a correlation between social exclusion and SUD. One study introduced non-drug-using and cocaine-seeking individuals to Cyberball, a virtual ball-tossing game. Throughout the game, the participants are gradually “excluded” from the game as the virtual players stop tossing the ball to them. The study found that differences in brain activity between cocaine users and non-users were most strongly exhibited in the anterior middle cingulate cortex, a region involved in the integration of pain and the perception of pain as negative (Hanlon et al., 2019). These results suggest that substance-addicted individuals are more vulnerable to the effects of social exclusion than non-drug-using individuals.

As such, drug addiction cannot be pinpointed to singular factors of risky environment, genetic predisposition, or moral character. Intimate social connections, which have the strongest correlation with happiness as shown by the Harvard Study of Adult Development, play a significant role in the progression of substance addiction. Although many would view the existence of risky neighborhoods as a challenge too large for one person to feasibly tackle, with the knowledge that a meaningful bond with at least one other individual can rescue a person from SUD, people may be more motivated to personally aid those whom they know are suffering from drug addiction. Above all, the research signifies that, entrenched in the stigmas surrounding drug addiction, individuals suffering from substance use disorder are nonetheless capable of change if only the people closest to them possess the empathy and knowledge necessary to lend a hand.

http://www.theharvardbrain.com/spring-2024-david-an.html