Addiction

Dr. Benjamin Rush, a founding father of the United States and a signer of the Declaration of Independence, is credited with first describing alcoholism as a “disease” in 1784. Prior to Dr. Rush’s writings on addiction, drunkenness was viewed as a moral defect and solely a matter of choice. Rush believed that the alcoholic lost control of his behavior or had what he called “an illness of the will”. He identified the properties of alcohol, rather than the individual's choice, as the causal agent. He also proposed that alcoholics could be treated by weaning them off of their addiction using less potent substances (similar to the way that methadone is used for heroin addiction today) and that total abstinence was the only effective cure.

Over a lifetime, many people use substances that have the potential for dependence, but most people do not become dependent. What is it that causes recreational substance use in some people to become uncontrolled, compulsive drug taking in others? The answer may have to do with how our brains respond to pleasure and rewards.

Have you ever wondered why you enjoy certain activities and aren’t particularly interested in others? Things you enjoy are rewarding to you. In other words, they bring you pleasure, a sense of well-being and reduced stress. All thoughts and behaviors have some biological component, and reward and pleasure are no exception. God has created within our brain a system that brings about a pleasurable experience when it is activated. Because we enjoy pleasurable experiences, we are more likely to repeat actions that activate our reward system. Many things can activate our reward system, from food to sex to alcohol and illicit drugs. For instance, food has been shown to increase activity in the reward system by 45 percent, whereas amphetamine and cocaine increase the activity by 500 percent. Commenting on this result, my graduate school pharmacology professor once said, “Cocaine takes your brain to a place it was never supposed to go, a place you will always try to get back to.”

Imagine a person with a dysfunction in his or her reward system that causes the system to be under activated. Things are not as rewarding to that individual as they are to the normal person. In neuroscience we call this condition Reward Deficiency Syndrome. Reward Deficiency Syndrome can result from an inherited genetic abnormality or from environmental factors such as trauma or stress. Research has shown that individuals with Reward Deficiency Syndrome begin to seek out experiences that will increase activity in their reward system. If they experiment with alcohol or illicit drugs, initially they find the pleasurable experience they were seeking. But after some time, which will vary across individuals and substances, a vicious cycle develops in which the consumption of alcohol and/or illicit drugs is no longer a choice or a pleasure but a necessity. The person becomes physically dependent on the substance and must take the drug to keep from experiencing painful and sometimes life-threatening withdrawal symptoms. While the positive, pleasurable state produced by the drug may have motivated initial use, continued use results in another motivation: relieving the negative, painful consequences of not using the drug.

While brain chemistry clearly plays a part, the underlying biological causes of the substance use disorders are much broader than any one neurotransmitter system. The reward system I have described above involves a number of brain structures, including the hypothalamus, amygdala, ventral tegmental area, substantia nigra, and nucleus accumbens. The nucleus accumbens, a structure deep within the middle of the brain, is considered by neuroscientists to be the brain’s central reward center. The cells in this brain structure are activated by the neurotransmitter dopamine (DA). When DA is released in the nucleus accumbens, the results are increased feelings of well-being and reduced stress. Substances such as alcohol, cocaine, heroin, PCP, marijuana, and nicotine all cause DA to be released in the nucleus accumbens, and thus they are potentially addictive. In addition, the neurotransmitters serotonin and GABA (gamma-aminobutyric acid) also appear to play a role in the brain’s reward system. Substance abuse and dependence involve a complex interaction between the physiological effects of drugs on the brain’s reward system and the learning of compulsive patterns of drug-seeking behaviors, both of which have a biological basis.

Research suggest that, much like the other behaviors I have discussed thus far, a genetic predisposition for addiction can be inherited from one’s parents and grandparents. Several studies have found that the child of an addicted parent is about four times more likely than the general population (where the risk is 1 in 12) to develop substance abuse or dependence themselves. This holds true even if the child of the addicted parent is adopted early and subsequently raised by adoptive parents who do not use alcohol or drugs.

As might be expected, a significant amount of genetic addiction research has focused on genes that are associated with the brain’s dopamine system. Alcoholism researcher Ken Blum and his colleagues have shown that a defect in the gene that codes for the dopamine D2 receptor is associated with the presence of substance use disorders. There research found that an individual with such a genetic defect has a 74% chance of developing Reward Deficiency Syndrome. It is important to remember that unlike diseases such as hemophilia, sickle-cell anemia and cystic fibrosis, which are caused by a defect in a single gene, behaviors like addiction are genetically complex and are likely to result from defects in many different genes.