There are many different kinds of addictions, from drugs to interpersonal relationships. Although these diverse addictions vary in many ways there are common threads that bind them together. There are several theories that model addiction: genetic theories, exposure theories (both biological and conditioning), and adaptation theories. To be successful, an addiction model must blend the multidimensional aspects of addiction. It must account for regional and cultural variation, interpersonal preferences as well as hold true for the variety of addictions. In addition, a good model will describe a cycle that exists that encourages increasing use until the addiction is overwhelming and leaves the host lame. Lastly, theories must be able to describe addiction as it occurs through human experience. Although animal studies can aid in understanding behavior, results need to be carefully interpreted before they are applied to the much more complex nature of a human being.

Genetic Theory

The genetic theory of addiction, known as addictive inheritance, attempts to separate the genetic and environmental factors of addictive behavior. Studies have been done to control for environmental components to determine if genetics plays a greater role. Most studies looking at alcoholism have determined that children born from alcoholic parents who are adopted into non-alcoholic families have a three to four fold increase in the rate of alcoholism over the rest of the population. Indeed, children born and raised by alcoholic parents have an even greater rate of alcoholism. This suggests that there is some genetic predisposition to alcoholic addiction.

Though a genetic component seems likely, exactly what the gene codes for has not been elucidated. Questions arise as to whether or not it is the addictive behavior that is encoded or a biological mechanism that drives the behavior. Are there differences in the metabolism of various addictive substances that allow an individual to have varying levels of a drug in the blood stream and have a psychological experience different someone else? Is there some genetic difference that perhaps allows some to realize when an elevated blood alcohol level has been reached and transmits a message to the brain to stop drinking that others do not have? These questions have not been clearly answered and are under persistent investigation.

One aspect of inheritance that is understood is that amongst members ofparticular races. Eskimos, American Indians, and Asians, for example, are all genetically predisposed to have a deficiency in the production of acetaldehyde, an enzyme important foralcohol degradation. Genetically similar in this regard, these groups are hypersensitive to the affects of alcohol. They respond immediately and intensely to the alcohol in their system. A characteristic flushing, known as Asian flushing, ensues once higher levels of alcohol are reached. Although this metabolic process is similar in all of these races, the addictive behavior is quite different. Eskimos and American Indians have a higher rate of alcoholism than Asians and are also predisposed for other addictive behaviors such as gambling that is not seen in Asians. This has raised the question as to whether or not a single gene can encode for multiple addictive behaviors, or if the maintenance of one addictive behavior allows for other addictions to arise more easily.

Finally, the strongest correlation between addiction and genetics comes when evaluating the pattern of inheritance. All studies show that it is sons, not daughters, who most often inherit the risk of alcoholism. How much of this phenomenon has its basis in genetic is not clear. Could it be that sons model themselves more after their fathers? Or is there a sex-linked genetic mechanism at play that is contributing to this phenomenon? As research continues, the role that genetics plays in addiction will be better understood. As of yet, it is sure to be a major component of most addictions and at the very least will predispose individuals to indulge in addictive behavior.

Exposure Theories: Biological Models

The exposure model is based on the assumption that the introduction of a substance into the body on a regular basis will inevitably lead to addiction. The biological, as opposed to the conditioning models, believe that this is a consequence of biology. Underlying the exposure model is the assumption that the introduction of a narcotic into the body causes metabolic adjustments requiring continued and increasing dosages of the drug in order to avoid withdrawal. Although changes in cell metabolism have been demonstrated, as of yet they have not been linked with addiction. Some theorize that those drugs that mimic endorphins (naturally occurring pain killers), if used on a regular basis, will reduce the body's natural endorphin production and bring about a reliance on the external chemical agent for ordinary pain relief.