Addictive Drugs & the Brain

Townsend Letter for Doctors and Patients,  July, 2001  by Jule Klotter

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Neuroscientists, using MRI and PET scans, have found that the use of addictive substances increases the amount of the neurotransmitter dopamine in the brain's pleasure centers. Some substances, like heroin, nicotine, alcohol, and amphetamines, cause neurons to release more of the pleasure stimulating dopamine than normally happens in everyday life. In addition, amphetamines, as well as cocaine, increase dopamine levels by inhibiting the action of the transporter molecules that remove dopamine from an area.

When dopamine levels are artificially over-stimulated for a period of time, the number of dopamine receptors diminishes as the brain attempts to calm down. With fewer receptors to pick up dopamine molecules, it takes more stimulation to produce feelings of pleasure. Addicts find that they need to take higher doses of a drug in order to experience the same euphoria that smaller doses had once given them. Eventually, the drugs no longer stimulate pleasure; they simply stave off feelings of anxiety and despair. Animal studies show that dopamine receptors will eventually return to normal with abstinence (which can be painfully difficult); but evidence also shows that drugs (i.e. cocaine) can inactivate the gene responsible for making a dopamine receptor. In addition, Pavlovian responses to a situation or sensory experience that an addict associates with drug use can bring on cravings for the drug, further complicating recovery.

"How It All Starts. Inside Your Brain" by Sharon Begley. Newsweek, February 12, 2001

COPYRIGHT 2001 The Townsend Letter Group
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