Return to Substance abuse articles

The disease of addiction has many factors but the most important reason underlying the use of drugs is that they make us feel good; we get high. We are temporarily rewarded for the behavior of using drugs.  Not only that, but any one who has ever experienced relapse can tell you that the initial use of a drug or alcohol led to the second use and than the third use and so on and so on.  We refer to this property as reinforcement: the rewarding of a behavior causing it to be repeated. Indeed, this is the key element in the persistence of any addictive behavior. Although the range of addictive substances includes a variety of different chemicals with different biological activities, it seems that reinforcement, leading to continued use, is the result of a common physiology that exists for all drugs of abuse.

To understand how this works, you must know a little of how the brain works.  The brain is bunches of individual nerves that communicate with each other and which are arranged into distinct areas to serve specific functions.  When one nerve communicates with a second, it releases a chemical called a neurotransmitter into the space between them; this space is called a synapse.  The second nerve reacts after its receptor binds to this chemical.  Depending on which chemical is released, the activity of the second nerve can either increase or decrease. All drugs act either by affecting how much of a neurotransmitter is in the synapse or interacting directly with a receptor.  Whole areas of the brain can be excited or depressed in this fashion.

There is an area of the brain in which increased activity will be perceived as pleasurable.  We know that lab animals with electrodes planted in this area of their brains, given small electric shocks, will continue to seek this stimulation. They will ignore all other bodily needs such as eating, drinking and sex.  The pleasure they are apparently feeling reinforces whatever behavior is needed to continue the shocks. This area is called the Nucleus Accumbens and may be thought of as the pleasure center of the brain. Nerves, originating from other areas of the brain, project to this area.  These nerves will affect the activity in the nucleus Accumbens by releasing a neuro-transmitter called dopamine.  This causes euphoria.  Almost all drugs of abuse have been implicated in increasing activity in this area. Cocaine and other stimulants directly increase the amount dopamine in the synapse and quickly increase the activity of this area.  Heroin, pills, alcohol and even marijuana have been shown to increase activity as well.

In addition to dopamine, another chemical, beta endorphin will is also released.  This results in a feling of pleasure that is independent drom that caused by dopamine.

Research needs to be done to find out how the various drugs lead to neurotransmitter release.  We hope that treatments may then be developed to block the reinforcing properties of the various drugs.  This has already begun. A drug called naltrexone  blocks endorphin.  It affects the way heroin, marijuana and alcohol work. It prevents the high from these drugs.  When a person takes naltrexone, their drug use goes down.

S. Wasser MD 
written 4/97
Revised 2/25/06

Return to Substance Abuse Articles