What is Addiction, and What Causes it?

This paper reflects the research and thoughts of a student at the time the paper was written for a course at Bryn Mawr College. Like other materials on Serendip, it is not intended to be "authoritative" but rather to help others further develop their own explorations. Web links were active as of the time the paper was posted but are not updated.

Contribute Thoughts | Search Serendip for Other Papers | Serendip Home Page

Biology 202
2002 First Paper
On Serendip

What is Addiction, and What Causes it?

Tara Rajan

When a mother brings her young son along with her to a methadone clinic for her daily dose, each nurse and staff members looks upon the little boy with worry. Is this child in risk of falling into the same patterns simply because his mother will find it difficult to teach him differently? Or, is he predisposed to drug dependence due to his own DNA? While drug dependency has not yet been reduced to a few "undesirable" genes in the human genome, most, if not all, scientists will agree that the risk of drug dependence is largely heritable. Why does drug dependency depend on genetics, and are there environmental factors as well?

The first step towards understanding drug addiction is finding an acceptable definition of the affliction. Drug addition can be defined as a "compulsion to use alcohol and other drugs and the occurrence of withdrawal symptoms related to nervous system hyper excitability" (1). The nervous system grows dependent on the drugs in order to function, which creates a psychological need for the drugs. How does this develop?

Heroin, which is just one example of a drug to which the body can develop an addiction, originates from the juice of the opium poppy. It's effects the body's opiate receptors in the central nervous system act to reduce painful sensations. The opium receptors are proteins, which are located on the face of neurons along the nervous system (2). Researchers found through experiments with radioactive naloxone that the heroin binds to these receptors and in turn inactivates them. Heroin does this by mimicking natural molecules in the brain, such as endorphin and enkephalin, which also inhibit the receptors (2). Therefore the body grows accustomed to not making any of the natural products itself and becomes dependent on the drug in order to feel comfortable and relaxed. Withdrawal can set in as soon as 8 hours after previous heroin use, and can include any of the following symptoms: drug craving, restlessness, muscle and bone pain, insomnia, diarrhea and vomiting, kicking movements, goose bumps, and depression (3).

One question that arises from this discussion is, if heroin produces these effects on the central nervous system, then why are some people more likely to become addicted than others? Wouldn't everyone eventually become addicted to the drug? One possible answer to this question is that while everyone has the potential to develop a heroin dependency, some people may be more likely to do so, or may have a more severe problem with the addiction. For example, some people may have greater difficulty synthesizing endorphins and therefore would have more trouble forcing their bodies to make it on its own. In addition, some people are more likely to fall into depression which influences drug use. If a person has high cortisol levels to begin with (which influence depression), he or she may become more severely depressed and therefore have a more difficult withdrawal period (4).

It is also possible that heroin addiction is similar to alcohol dependence, which has been found to be genetic. For example, children of alcoholics are said to be 4 times as likely to become alcoholics as opposed to people without family history of alcoholism. However, part of this amount of risk can be accounted for by environmental influence.

In a study in Sweden, the alcohol habits of identical twins that were adopted and reared apart were examined. The incidence of alcoholism was slightly higher among people who were exposed to alcoholism only through their adoptive families. However, it was dramatically higher among the twins whose biological fathers were alcoholics, regardless of the presence of alcoholism in their adoptive families (4). This study suggests that alcoholism is influenced by biology and slightly by environment.

In another study being performed by Dr. Henry Kranzler of UConn Health Center, subjects are tested on their delay discounting rates (5). Delay discounting indicates whether people are likely to be able to wait for a period of time for a larger monetary reward, or whether they will take a smaller amount of money without being able to wait. For example, subjects are offered either 10 dollars today or 50 dollars in 2 days. The choices that they make demonstrate the type of personality they have, and whether they are more likely to fall into dependent habits such as drug addictions. These personalities have been found to be genetic, which could also link addiction to genetics (5).

The link between drug abuse and genetics seems to be one that is difficult to ever fully examine. However, drug abuse is probably influenced by a balance of genetic predisposal as well and environmental persuasion. While it may be possible for anyone to become dependent on alcohol or heroin, some people are more likely to develop an addiction than others. As Terence T. Gorski writes, "genes and environments are locked together in complex loops that affect each other. Certain environmental conditions stimulate the activity of certain genetic traits. Other environmental conditions inhibit the activity of certain genetic traits" (6). This means that genetics provides tendencies to act a certain way, yet these tendencies need to be activated in order to function properly. If the young boy had never been exposed to heroin, he would most likely never have a problem with a heroin addiction. However, the influence of his mother's addiction may activate his own disposal to a heroin dependency.


1)The Neurobiology of Addiction

2)The Opiate Receptor

3)Heroin Addiction

4)The Genetics of Alcoholism

5)Cocaine Addition Links

6)Psychology Abstracts

| Forums | Serendip Home |

Send us your comments at Serendip

© by Serendip 1994- - Last Modified: Wednesday, 02-May-2018 10:53:09 CDT