Heavy Pot Use Can Cause Physical Dependence

From the WebMD Archives

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. Find out why people think marijuana isn't addictive.


"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."


During the abstinence period, the participants reported increases in anxiety, irritability, physical tension, depression, and loss of appetite. The symptoms were most pronounced during the initial 10 days of withdrawal, but two of the symptoms -- irritability and physical tension -- remained high during the entire study period.


"This study shows that there are consequences to smoking marijuana on a regular basis," says Kouri. "Marijuana is not as benign a drug as a lot of people would like to think. But, at the same time, the withdrawal symptoms were not as severe as those routinely seen with other drugs of abuse, and they peaked at about 10 days. That is an important message, because if somebody is trying to quit and they know the crankiness and irritability will go away after the first week or so, they might be more likely to stick with it."


Lichtman says that marijuana withdrawal symptoms do not appear to be as pronounced as those seen with other drugs because THC has a long half-life -- about 30 hours in humans.


"Drugs that have a long half-life take a long time to be broken down, and withdrawal effects occur slowly," he says. "A lot of times, the effects are so subtle that the individual may attribute it to something else."