3.9.3 Drug addiction
Drug Use, Addiction, Tolerance, Withdrawal, and Relapse
A chronic brain condition, addiction. Addiction is also known as a substance use disorder when it is connected to drugs or alcohol. Although there is no cure for addiction, it can be managed with treatment. In this context, “drugs” refers to any substance that has an impact on the body. Prescription medications, over-the-counter items, illicit substances, alcohol, and even nicotine may be included.
Drug addiction is a more severe form of substance abuse that leads to issues not just while the user is using the substance, but also after they try to stop.
The neurobiology of addiction can be framed around a three-stage cycle: binge/intoxication, withdrawal/negative affect, and preoccupation/anticipation.
Dependence and addiction:
Another word that is frequently mixed up with the term addiction is dependence. Dependency simply implies that the body has grown reliant on receiving a drug from an outside source in order to avoid going through withdrawal. Most medications increase the number of specific brain chemicals, which has a pleasant impact.
Tolerance:
Tolerance can form when drugs like morphine or cocaine are used frequently over time. When a person stops reacting to a substance the same way they did at first, that is when tolerance sets in. Cellular tolerance happens at the molecular level. One way for this to happen is for the body to metabolise the drug more quickly so that it leaves the body more quickly than before.
Withdrawal:
Depending on the substance used and the regular dosage used, a person may experience a variety of physical and psychological symptoms associated with withdrawal, ranging from minor to life-threatening. It happens after the person has developed a drug dependence. This means that in order to avoid withdrawal symptoms, the user must gradually quit using the chemical.
Relapse:
Relapsing is the process by which someone who had been abstaining from drugs or alcohol for a while does so again. During the course of a person’s rehabilitation from substance misuse, addiction might relapse. Even though relapse is extremely prevalent among those in recovery, it is seldom generally discussed as a stage of the process.
The Role of Dopamine in Addiction
Drug addiction is fundamentally gratifying. They hijack the brain’s dopamine system in order to boost dopamine levels in the nucleus accumbens, which is a critical focus point for reward neurocircuitry in the brain.
Dopamine is a neurotransmitter in the brain that plays a crucial role in addiction. Dopamine is associated with pleasure and reward and is released in response to pleasurable stimuli such as food, sex, and drugs.
When a person uses drugs or engages in other addictive behaviours, the release of dopamine in the brain is significantly increased. Over time, the brain becomes accustomed to the elevated levels of dopamine and needs more of the substance or behaviour to produce the same pleasurable effects. This leads to the development of tolerance, which is one of the key features of addiction.
Drugs of abuse, such as cocaine, amphetamines, and opioids, are able to increase dopamine levels in the brain by either blocking the reuptake of dopamine or increasing its release. This leads to a surge of dopamine in the brain, producing feelings of pleasure and reinforcing drug-taking behaviour.
Long-term drug use can also alter the dopamine system, leading to changes in brain function and structure. This can result in a decreased sensitivity to dopamine and reduced pleasure in response to natural rewards, making it harder for an individual to quit using drugs and increasing the risk of relapse.
In conclusion, dopamine plays a crucial role in the development and maintenance of addiction by mediating the pleasurable effects of drugs and other addictive behaviours. Understanding the role of dopamine in addiction is important for the development of effective addiction treatments.
The rate of dopamine increase plays a factor in whether a drug or substance will produce a rewarding effect. The prefrontal cortex contains both D1 and D2 dopamine receptors. D2 receptors have a 10-100x greater affinity for dopamine compared to D1 receptors.
Learning Mechanisms Underlying Addiction
Initially, drug use is a deliberate, goal-directed behaviour. People utilise drugs in order to achieve a specific high or reward. In other people, however, the conduct becomes compulsive and is no longer related to the pursuit of a reward. This modification is linked to a change in brain circuitry. While areas such as the basolateral amygdala and the nucleus accumbens are required to acquire persistent drug-seeking behaviour, they become less significant once the habit is established. The dorsolateral striatum then becomes increasingly essential. A significant rise in dopamine is detected in the dorsal striatum of animals engaged in long-term drug-seeking behaviour, but not in the nucleus accumbens core or shell.
Blocking dopamine receptors in the dorsal striatum, but not in the nucleus accumbens, has been shown to diminish well-established, habitual drug-seeking behaviour.
References:
(1) Uhl, G.R., Koob, G.F. and Cable, J. (2019). The neurobiology of addiction. Annals of the New York Academy of Sciences, 1451(1), pp.5–28. doi:10.1111/nyas.13989.
‌(2) Wise, R.A. & Koob G.F.. 2014. The development and maintenance of drug addiction. Neuropsychopharmacology 39: 254–262.