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Substance Abuse and Addiction Health Center

Heavy Pot Use Can Cause Physical Dependence

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WebMD Health News

Nov. 27, 2000 -- Heavy marijuana users who stop cold turkey experience a host of withdrawal symptoms, including irritability, anxiety, and depression, but most symptoms begin to lessen after 10 days or so, a study from Harvard Medical School suggests.

Reported in the November issue of the journal Experimental and Clinical Psychopharmacology, the study is the first in humans to examine marijuana withdrawal in a setting outside the laboratory. Participants agreed to give up smoking pot for a month, and they submitted to daily urine tests to make sure they stayed drug free. But with the exception of not smoking marijuana, they continued their normal activities.

There has long been controversy over whether daily pot smokers actually become addicted to marijuana and whether withdrawal symptoms are real. Recent animal studies and studies evaluating the use of cannabis in humans under laboratory conditions support the notion that marijuana withdrawal syndrome exists.

"A few years ago, it was widely believed that marijuana does not cause any kind of physical dependence, but now that has pretty much been debunked," Aron Lichtman, PhD, of Virginia Commonwealth University, tells WebMD. "Studies like this one and the ones we have done show that physical dependence does exist." Lichtman and colleagues from Virginia Commonwealth have conducted numerous animal studies on the effects of THC, the active ingredient in marijuana.

In the Harvard study, researchers recruited 60 active marijuana users between the ages of 30 and 55 who reported smoking at least five times a week for an average of 11 years. Half of the participants agreed to stop using pot for 30 days, and the other 30 served as controls. In addition to the daily urine tests to evaluate compliance, participants filled out a 14-item daily diary designed to track changes in mood and physical symptoms. They were also tested for anxiety and depression levels before the study began, and again on days 1, 7, and 28 of the study period.

"They had to be willing to come in every day, even on the weekends," lead author Elena M. Kouri, PhD, of Harvard Medical School, tells WebMD. "I think most of them did it because they wanted to prove to themselves or to someone else that they could stop smoking for a month."

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