Biological Influences on Drug Use

Substance abuse, also known as drug abuse, has multiple definitions. Generally, it is loosely defined as usage of an illicit, or prescription drug, that negatively affects the functional status of a person.

There are multiple questionnaires currently used to screen for drug abuse, such as the Cut, Annoyed, Guilty, and Eye (CAGE) questionnaire for alcohol screening. However, using recreational drugs even without a functional decline can still be considered substance abuse.

The CAGE questionnaire is a four-question alcohol-screening tool.

• C – Have you ever thought of cutting down on your drinking?
• A – Have you ever been annoyed by criticism of your drinking?
• G – Have you ever felt guilty about your drinking?
• E – Have you ever had any eye-openers?

A score of 2 or greater, meaning the patient answered yes to two of the following questions, has a 93 percent sensitivity and 76 percent specificity of excessive drinking, and a slightly lower sensitivity for alcoholism.

Substance abuse can be harmful to the person it afflicts, and may cause significant interpersonal problems. Furthermore, drug abuse and addiction can have legal ramifications as well. Thus, it is imperative for treating physicians to be aware of the factors which affect drug use such as biological influences.

Biological Influences on Drug Use

Thanks to neurobiology and much of the research that has stemmed from this field, we now know quite a bit regarding the biological influences of drug use. Though there are multiple social and socioeconomic factors that can influence drug use, we will be focusing on biological influences. There may of course be overlap between multiple different factors.

Some of the biological influences on drug use include:

1. Genetics
2. Family History
3. Neuro Development
4. Neuro Anatomy

When looking at the biological influences on drugs, it is important to assess all these separate components and assess the interactions each component may have.

Addiction

Addiction is a physiological or psychological need for a substance, behavior, or activity. The American Society of Addiction Medicine, perhaps controversially goes as far to describe addiction as a chronic brain disease. Though when most people think of addiction, drugs may be the first thing they think of, people can be addicted to many different things. For instance, some people have an addiction to gambling, or even to their cell phones. Let's take a look at genetics. According to ASAM, it is possible that genetics accounts for close to 50 percent in determining whether or not someone will develop an addiction. There have been researched outputs that have highlighted certain genes seen more in people who have a higher predisposition to alcohol abuse. It was found that these genes affect the dopamine system; it is known that dopamine plays a role in addiction. Thus, it is possible that these changes play a significant role in the development of addictive illnesses.

There is a high co-occurrence of mental health disorders with substance abuse disorders: Depression, bipolar, anxiety, and so on. In fact, patients with schizophrenia are more likely to have nicotine disorders. This indicates and supports the concept that organic causes of drug use are likely.

Examples of Biologic Influences on Drug Use

One great example can be seen through twin studies. It was found that identical twins are most likely to either both be alcoholic, or neither. Furthermore, studies of children born to parents with alcohol issues who were adopted by parents who did not have alcohol addiction problems, remained at higher risk of developing alcohol problems themselves, against those who were born to parents without a history of alcohol addiction.

Influence of Drug Use on the Brain

Though it is postulated that people may be more predisposed to developing addiction, it is also theorized that using drugs also affects addiction as well. It seems there is a feedback loop; the more substance taken in, the greater the possible addiction. It may even be that addiction can physically change certain areas of the brain, basically destroying the proper physiologic functions.

Certain conditions such as Wernicke-Korsakoff syndrome are severe, as seen in patients with chronic alcoholism. The patient may develop severe amnesia among other problems. However, there are more subtle changes that occur with drug use as well.

In a healthy person who does not have an addiction, the brain rewards behaviors like exercising, or engaging in relationships with friends or family. It is also true that the brain has impulses, but these impulses can be mitigated by the frontal cortex, which is the area mainly responsible for decision-making.

When a person becomes addicted to drugs, their reward system is affected. The reward they feel from relationships or exercise, for example, don’t compare to the reward they may feel from drugs. They continue using drugs to feel that reward.

Brain imaging has even shown the decreased volume of the frontal cortex in people affected by addiction, indicating less of a decision-making capacity.

Influence of the Nucleus Accumbens on Drug Addiction

The nucleus accumbens is one of the major input structures of the basal ganglia. Its job is to integrate information from the cortical and limbic areas of the brain to assist in goal-directed behaviors. It was found that chronic exposure to drugs and substances affected the plasticity of the nucleus accumbens.

Nucleus Accumbens Sagittal View - commons.wikimedia.org

In the current research, it seems that glutamatergic transmission within the nucleus accumbens is affected after withdrawal from chronic drug exposure. Furthermore, it is thought that the changes that occur within the brain, specifically within the nucleus accumbens, contribute to the potential for relapse after the patient attempts to quit.

Influence of the Orbitofrontal Cortex on Drug Addiction

The orbitofrontal cortex is the area in the brain that is thought to provide control to our behaviors. It has a large part in the decision-making process.

Frontal Lobe Lateral View - commons.wikimedia.org

The current literature states that deficits in reward processing are implicated in abuse disorders. Volume reduction in the orbitofrontal cortex, as well as other areas such as the striatum, is further implicated in abuse disorders.

Finally, studies that used brain imaging looked at the orbitofrontal cortex, and found that this area is altered in people with drug addictions.