Monkeys on Marijuana Wanted More

A new federal study shows that monkeys will dose themselves with the main active ingredient of marijuana repeatedly. Researchers say this evidence strengthens the theory that people can become addicted to pot and provides a new way to test therapies.

Lab animals will actively dose themselves with most drugs abused by people, but marijuana has been an exception, said researcher Steven Goldberg of the National Institute on Drug Abuse (NIDA).

Some people might interpret that as suggesting it has little potential for addiction, he said. But the new work found that squirrel monkeys repeatedly pushed a lever to get injections of the marijuana ingredient THC, Goldberg and colleagues report in the November issue of the journal Nature Neuroscience.

The animals pushed the lever about as much as other monkeys did to get cocaine, but Goldberg said that does not necessarily mean marijuana is as addictive as cocaine in people.

Causes Compulsive Craving

NIDA says marijuana causes compulsive and often uncontrollable craving and use, despite health and social consequences, and therefore is addictive.

Not everybody agrees.

“This drug is not addicting. Clinical experience says that,” said Dr. Lester Grinspoon, a Harvard Medical School emeritus professor of psychiatry.

The monkey study doesn’t prove otherwise, said Grinspoon, who is chairman of the board of the NORML Foundation, which promotes medical use of marijuana and, ultimately, its legalization.

In Goldberg’s experiment, four squirrel monkeys sat through hour-long test sessions once a day with a tube attached to a vein. When a green light turned on, they could push a lever 10 times to get a THC injection.

They gave themselves up to 30 injections per session, versus one to four when the tube delivered only water.

In proportion to their body size, the monkeys got about the same dose of THC per injection that a person does with each puff from a marijuana cigarette. The monkeys didn’t show any sign of being sedated, Goldberg said.