Source: From New Scientist
Date: 21 October 2000

Hooked on hash
Monkeys stir up the debate about cannabis addiction

squirrel monkeys and cannabis

The question of whether marijuana is physically addictive has been troubling researchers for years--but the latest evidence suggests that lab monkeys, at least, are easily hooked.

For the first time, scientists in the US have shown that monkeys will seek out the active chemical in cannabis just as they would with cocaine or morphine. The finding has created an uproar over the implications for humans who smoke pot.

Therapists and psychiatrists who treat marijuana dependency are convinced the study will persuade people to take pot's potential for abuse more seriously. "A lot of people think it's not addictive," says Ron Kadden of the University of Connecticut Health Center. "[Users] have been told by treatment professionals and friends that they couldn't really be addicted to marijuana." But Kadden says he recently found plenty of takers when he advertised a programme tailored to treat cannabis dependency.

Campaigners for the legalisation of dope, on the other hand, have called the study "pseudoscience", designed to fulfil a political agenda. "We take umbrage with the government's seemingly never-ending penchant to prove that cannabis is harmful enough to justify the 70-year prohibition," says Allen St Pierre of the National Organization for the Reform of Marijuana Laws in Washington DC.

Last week, a survey showed that one in ten people in England and Wales has used cannabis in the past year. The report from the European Monitoring Centre for Drugs and Drug Addiction says that cannabis is regularly used by 45 million Europeans.

However, proving that marijuana is addictive like cocaine or even nicotine has been difficult. For years, scientists have been unable to get animals to give themselves THC, the active chemical in marijuana.

In the latest attempt, Steven Goldberg and his colleagues at the National Institute on Drug Abuse in Baltimore, Maryland, gave squirrel monkeys a small injection of THC every time the animals pressed a lever. The monkeys quickly learned to give themselves as many as thirty injections of the drug in a one-hour session.

Giving the animals a drug that blocks the brain's cannabinoid receptor, however, stopped the monkeys pressing the lever. "We're interested in looking at potential compounds that might be used as medications for drug abuse," says Goldberg. "Now that we have a model of how THC supports drug behaviour we can go in and try to intervene."

The researchers say they know why their experiments succeeded where others had failed. They gave the monkeys as much THC as you would get from a single puff on a joint--with the dose adjusted for the animals' body weight. This meant the monkeys took doses of THC that were five-fold less than scientists have tried in the past.

People who have trouble quitting may take comfort from the study, says Elena Kouri of Harvard Medical School. She has studied withdrawal symptoms like tremors in people who have smoked pot daily for years. "If we educate them that it's not that they don't have the willpower, that it's the drug, I think it will help them go through the withdrawal."

Nell Boyce, Washington DC

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