Marijuana’s active ingredient may cause addiction
By Steve Sternberg

USA TODAY

Years of pot smoking may alter brain chemistry so that deprivation provokes anxiety of the sort that follows withdrawal from alcohol, nicotine and cocaine, researchers report today.

The observation was made in rats, not humans. And the researchers used HU-210 a synthetic form of marijuana's active ingredient, not marijuana itself. Nevertheless, the findings, reported in the journal of Science, are the latest suggesting that drugs linked to abuse trigger the same cascade of chemical events.

"We've become convinced in the last year that although every abusable drug works in its idiosyncratic way, all share common characteristics," says Alan Leshner, director of the National Institute on Drug Abuse, which funded the HU-210 study.

"What we're beginning to understand is that drugs of abuse activate natural reward mechanisms that already exist in the brain," says Steven Childers of Bowman Gray University in Winston-Salem, N.C.

The new research, by George Koob and colleagues at Scripps Research Institute, La Jolla, Calif., found that HU-210 injections slowed to a trickle the rat’s production of the brain chemical corticotrophin-releasing factor (CRF), which is linked to anxiety. When scientists blocked HU-210's effects after two weeks of steady injections, the rats' CRF output surged - and their agitated behavior betrayed signs of withdrawal.

In another report in Science, Gaetano Di Chiara and colleagues at the University of Rome, Italy, found that heroin and marijuana-like substances both sent the brain chemical dopamine coursing through a part of the brain linked to addiction. Dopamine is thought to produce the pleasure that rewards drug abuse.

The study suggests that marijuana activates the same reward centers as heroin. Childers, a pharmacologist expressed surprise at this result. Because marijuana doesn't foster the intense dependence of drugs known to trigger dopamine release, he says, "It's not what we would have predicted."

Nevertheless, Childers says, the new studies are exploding "the old concept that drug abuse is a moral problem. Now we understand that it is a brain disease we can study."

Copyright, 1996, USA TODAY, Reprinted by permission.