Marijuana 'is as addictive as heroin'

A study into the addictiveness of cannabis has concluded that the drug can be as compulsive as cocaine or heroin. The findings will come as a blow to those campaigning for the legalisation of marijuana.

A study into the addictiveness of cannabis has concluded that the drug can be as compulsive as cocaine or heroin. The findings will come as a blow to those campaigning for the legalisation of marijuana.

The research by Steven Goldberg, of America's National Institute for Drug Abuse near Washington, used a standard test for addictiveness in laboratory animals and found little difference between the effects of cocaine, heroin and cannabis.

The study, published today in the journal Nature Neuroscience, used a technique called self-administration behaviour, where laboratory animals have a free choice on whether to take small quantities of a drug intravenously.

Dr Goldberg's team used squirrel monkeys which had an intravenous catheter attached to a lever that they had to press 10 times before being receiving small doses of the drugs. If animals repeatedly press the lever, this is taken as evidence of the drug's addictiveness.

Previous studies have failed to show that cannabis led to such behaviour, but used far higher doses than those received by smoking a cannabis joint. Dr Goldberg's research used a much lower dose, and found the monkeys injected themselves compulsively in almost the same way as when given the option of injecting cocaine or heroin.

"The active [ingredient] of cannabis possesses strong reinforcing properties," Dr Goldberg said. "We've shown in this animal model that cannabis behaves in the same way as cocaine and heroin."