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Marijuana and Depression

USC College study finds no link between symptoms of depression and regular marijuana use.

By Pamela J. Johnson
December 1, 2005

Marijuana and Depression

Marijuana smokers are less depressed than those who never smoke, purports the largest-ever study of its kind, co-authored by a USC College psychology researcher. The conclusions surprised even the study’s co-author.

College doctoral candidate Tom Denson co-authored the study on marijuana and depression to be published in the journal, Addictive Behaviors.

Denson wrote the report with psychologist Mitch Earleywine, a former College associate professor and author of Understanding Marijuana (Oxford University Press, 2002). Earleywine is now a faculty member at the University at Albany.

Inside Denson’s USC office overlooking downtown Los Angeles, the fourth-year Ph.D. student said the findings startled him.

“I thought that at least the medical-marijuana users might be more depressed,” Denson, 30, said. “If they already had a medical condition, I thought they might be more susceptible to depression.”

While the study found that those who smoke marijuana for medical reasons were more depressed than other smokers, they were less depressed overall than nonsmokers.

Rather, daily or weekly marijuana users — including those smoking the drug for medical rather than recreational reasons — had fewer symptoms of depression than nonusers. Further, marijuana users were more likely to report positive moods and fewer somatic complaints such as sleeplessness, poor appetite and trouble completing their daily routine, the study stated.

The Internet study questioned more than 4,400 marijuana users and non-users. The researchers said the online study made it possible to include the severely depressed or those who would not participate in an in-person or telephone survey about an illicit drug.

Although some have suggested that participants may give bogus answers in online studies, Denson said, “that’s not restricted to the Internet.”

“That’s a weakness any time you ask anyone a question, whether it’s online, over the phone or in-person,” he said. “In fact, I think it’s a strength of the study because I think people feel more comfortable answering questions about deviant behavior when it’s anonymous.”

Participants were divided into three categories: daily and weekly smokers, and non-smokers. To assess levels of depression, they used the Center for Epidemiologic Studies Depression scale in which participants answered a series of questions describing their moods.

The study was the first to compare depression rates in medical-marijuana users and non-medical users.

"Those who use marijuana to battle the symptoms of illness may be depressed because of their illness, not because of marijuana," Earleywine said. "Studies that do not identify medical use might falsely implicate marijuana, rather than sickness, as the cause of depressed feelings."

After a story about the study appeared in the Nov. 18 Albany Times Union, Denson received correspondence from researchers who said their similar-smaller scale studies resulted in the same findings.

The findings don’t mean marijuana alleviates depression, Denson said.

“We’re not encouraging smoking,” Denson said. “There are many treatments for depression. Cognitive behavioral therapy works very well.”

He acknowledged that the findings might be controversial and even the subject of jokes. During The Tonight Show recently, host Jay Leno talked about Denson’s study during his monologue.

Leno told the audience that according to the new study, marijuana doesn’t cause depression. “Oh yeah?” Leno said. “Just wait until they take away their marijuana.”