It’s widely believed that marijuana is not addictive, but a major new evidence review suggests that’s not true.

Not only can people suffer withdrawal symptoms when they quit pot, but nearly half of those who regularly or heavily use marijuana will go through withdrawal when they stop, according to the study published online April 9 in JAMA Network Open.

About 47% of frequent users seeking treatment experience what’s dubbed cannabis withdrawal syndrome, according to pooled results from 47 studies that included more than 23,500 participants.

“The results suggest that withdrawal is likely or possible for a large majority of users, particularly heavy users,” said Emily Feinstein, executive vice president of the Center on Addiction, in New York City.

“People should be prepared to experience withdrawal if they are going to stop using marijuana, and ideally consult a health care provider to help manage the symptoms and reduce the risk of relapse,” added Feinstein, who was not involved with the study.

Marijuana withdrawal symptoms include nervousness, anxiety, sleeplessness, depression, restlessness and irritability, said Dr. Timothy Brennan, director of the Addiction Institute of Mount Sinai, in New York City.

People quitting pot also might experience physical symptoms like stomach pain, shakiness, tremors, sweating, fever, chills and headaches, he said.

“It can be miserable, and presents a challenge for people trying to get sober from cannabis,” Brennan said.

Experts have long argued that marijuana withdrawal is a real phenomenon, but these concerns received a new legitimacy with the 2013 publication of the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), Brennan said.

The DSM-5, considered the bible for psychiatric diagnoses, recognized cannabis withdrawal syndrome as a bona fide disorder.

Brennan, who was not involved with the study, said it’s likely that withdrawal is occurring more often because today’s pot is much more potent than before.

“The cannabis supply that’s out there now compared to the cannabis supply that was around in the 1960s and 1970s shows a dramatic increase in the percent of THC,” the chemical in pot that gets you high, Brennan said. “The cannabis now is much stronger, and that’s what people develop a dependence on and a withdrawal from.”

Cannabis withdrawal syndrome is more common in men and in people who use tobacco or other drugs along with pot, according to the new analysis by Dr. Anees Bahji of Queen’s University in Ontario, Canada, and colleagues.

Heavy users are also more likely to experience withdrawal.

Feinstein pointed out that “there is no clear line that suggests how much use will cause withdrawal, and it will differ from person to person, but generally the data suggest that the likelihood of withdrawal increases with intensity of use and severity of addiction.”

Paul Armentano is deputy director of NORML, which advocates legalization of marijuana. He said symptoms of withdrawal tend to be mild and short-lived, particularly when compared to those associated with other substances that are legal nationwide.

“By comparison, the profound physical withdrawal effects associated with tobacco are so severe that many subjects who strongly desire to quit end up reinitiating their use,” Armentano said. “In the case of alcohol, the abrupt ceasing of use in heavy users can be so severe that it can lead to death. Simply withdrawing from caffeine can lead to a number of adverse side effects, like rebound headaches.”

Brennan agreed. “Most symptoms go away in a few days,” he said. “Nearly all symptoms go away in a few weeks.”

But marijuana users need to be convinced that their symptoms are occurring because they’re quitting pot, or they’re liable to relapse, said Dr. Scott Krakower, unit chief of psychiatry at Zucker Hillside Hospital in Glen Oaks, N.Y.

“People may feel that weed helps their anxiety level, but it may be more that you are developing worsening anxiety from marijuana withdrawal, rather than weed helping your anxiety level,” Krakower said. “It’s hard to explain to people that the symptoms they’re experiencing could be from them not using marijuana.”

Meanwhile, Brennan said folks experiencing symptoms of marijuana withdrawal should hang tough, and take over-the-counter remedies for physical ailments like nausea and headache.

“It does get better, and the symptoms do go away with time,” he said. “If they know there’s light at the end of the tunnel, maybe that will help motivate them to stick with it.”

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