WHY DRUGS PLEASE HUMANS

In 1995, 12.8 million Americans reported that they had used illicit drugs
in the previous month, according to the National Household Survey on Drug
Abuse. This number is down considerably from a peak of 25 million in 1979,
which is a positive sign. But reducing the number to zero may be an
impossible goal, according to new research by Randolph Nesse, a
psychiatrist at the University of Michigan Institute for Social Research
and Medical School.

Most drugs of abuse work on ancient brain mechanisms that may have evolved
between 600 million and 1 billion years ago. The drugs convey to the system
a health benefit that has not occurred. "When a recent article suggested
that marijuana worked on dopamine receptors in a similar way to cocaine,
some critics said, 'but so does sex, and so does chocolate,'" says Nesse.
"And they do. But when you stimulate with a natural substance, there are
built-in dampening mechanisms that are bypassed when substances work
directly on the brain."

The refinement of modern drugs amplifies the problem. "Drugs have been with
us for a long time," says Nesse. "But there previously has not been the
purity, availability, and delivery we have now. It's almost like a new
virus that we haven't evolved defenses to yet."

For more information on Nesse's research, see "Psychoactive Drug Use in
Evolutionary Perspective," in the October 3, 1997 Science, available at
http://www.sciencemag.org.

Copyright 1998 © Cowles Business Media.