The Biology of Addiction: Voluntary Behavior and Genetics
Bertha K. Madras, Ph.D.
Deputy Director, Demand Reduction
Office of National Drug Control Policy
The brain is the repository of our humanity; our wisdom; and our ability to amuse, build, compose, compute, contemplate, create, design, draw, and learn. It enables us to discover colliding galaxies, the genetic code, and new medicines; to feel disappointment, empathy, joy, motivation, pain, and pleasure; to remember; and to engage in justice, compassion, and mercy.
| Adolescents are particularly vulnerable to the effects of drugs. |
Addiction science is helping us to better understand how drug use jeopardizes this vital organ. For example, we know that certain drugs, such as cocaine, methamphetamine, ecstasy, and alcohol, create toxic reactions in the brain, destroying nerve cells or nerve endings and compromising blood supply. Drugs can change cell structure, metabolism, circuitry, and brain signals. As addiction sets in, an entire set of behaviors, such as waking up, washing, eating, dressing, going to school, and focusing on commitments and goals, can become secondary as the brain focuses on a narrow drug-seeking path—despite adverse consequences. A brain that has adapted to a drug-centered existence but no longer has a steady drug supply can coast gradually or slide rapidly into withdrawal. Relapse to drug use can occur long after withdrawal symptoms have ceased, even years later.
Drug-induced brain changes are only some of the biological factors that drive drug use. Genetics also is a risk factor, albeit a very complex one. Genes may affect how quickly a drug is cleared from the body, how the body reacts to drugs, how difficult it is to quit, and the severity of the withdrawal process. Genes also may help to identify those people who are at higher risk for abusing drugs such as pain medications. By studying genes, we can begin to understand how addiction emerges and how to develop medications and other strategies to help treat addiction.
There is good evidence from family, twin, and adoption studies suggesting that genetic and environmental factors play equal roles in the development of addiction. For example, siblings of abusers are more likely to use drugs. Likewise, adopted children with histories of substance abuse in their biological families are more likely to become abusers themselves, even if the current environment is devoid of drugs. Identical twins have a higher propensity to share drug histories than fraternal twins.1,2
Among other research in the field of addiction science are studies scanning multiple genes at the same time—as many as 500,000 gene snippets simultaneously—to seek genetic differences between nonaddicted and addicted populations.3,4,5,6,7 More than 100 candidate genes for addiction have emerged from this approach, along with a few intriguing principles. It appears that genes involved in susceptibility to addiction are not necessarily unique to a single drug. This may help explain why some people abuse or become dependent on several drugs at the same time.
| Avoiding initiation is the key to preventing addiction in the first place. |
A number of treatment approaches such as cognitive behavioral therapy and medication-assisted therapy are effective in helping people override biology. Although recovery is possible, avoiding initiation is the key to preventing addiction in the first place. Random student drug testing is a drug abuse prevention strategy that can address both environmental and biological factors associated with drug use. Random testing sends a strong message to young people that drug use is dangerous; in addition, it can help promote a culture of disapproval toward drugs in the communities where it is employed. By giving students a reason to resist peer pressure to use drugs, the school norm becomes abstinence rather than use. Testing can identify adolescents who have started using drugs as well as students who already have become dependent on or addicted to drugs so that parents and counselors can intervene.
Adolescents are particularly vulnerable to the effects of drugs, and the earlier an adolescent begins using drugs, the more likely he or she will develop a substance abuse problem or the disease of addiction. As science makes headway in the field of addiction medicine, our understanding of the role that genetics plays in addiction will be further refined, and more effective treatment methods will be developed. Regardless of scientific progress, prevention is still the prescription.
Citations
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2Agrawal A, Lynskey MT. Are there genetic influences on addiction: evidence from family, adoption and twin studies. Addiction. 103(7):1069–81, 2008. PMID: 18494843.
3Uhl GR, Grow RW. The burden of complex genetics in brain disorders. Arch Gen Psychiatry.61(3):223–9, 2004. PMID: 14993109.
4Lachman HM. An overview of the genetics of substance use disorders. Curr Psychiatry Rep. 8(2):133–43, 2006. PMID: 16539891.
5Enoch MA, Goldman D. The genetics of alcoholism and alcohol abuse. Curr Psychiatry Rep. 3(2):144–51, 2001. PMID: 11276410.
6Uhl GR. Molecular genetics of addiction vulnerability. NeuroRx. 3(3):295–301, 2006. PMID: 16815213.
7Uhl GR. Molecular genetic underpinnings of human substance abuse vulnerability: likely contributions to understanding addiction as a mnemonic process. Neuropharmacology. ;47 Suppl 1:140–7, 2004. PMID: 15464133.