Marijuana is the most commonly used illegal drug, according to the study, citing a 2008 survey that found about 42 percent of high school seniors reported having tried marijuana. About 5 percent said they had used it daily during the previous month.
Though generally believed to be less addictive than nicotine in tobacco products, about 12 percent of marijuana users meet the criteria for dependency, according to the study. Symptoms of marijuana or alcohol dependency include using more heavily or more frequently than intended, giving up important activities to smoke or drink and building a tolerance or needing to use more to get the same effect.
Marijuana's active ingredient, THC, acts on the brain's cannabinoid system, which is involved in learning, memory, appetite and pain perception, explained Dr. Christian Hopfer, an associate professor at the University of Colorado School of Medicine. Medical uses for marijuana including alleviating pain and boosting appetite in people with cancer and other serious illnesses.
But marijuana has its downsides. Other research has shown marijuana use increases the risk of developing mental illnesses, Hopfer added.
Far less research has been done about marijuana than on tobacco or alcohol products, Hopfer said. That needs to change. Not only is marijuana use widespread, but THC levels in pot have increased in recent years, making the drug's effects more potent.
"We are quasi-legalizing it due to medical marijuana, yet we really don't know that much about it except a lot of people are self-administering it," Hopfer said. "Marijuana addiction is a subtler addition than with some other drugs, but it can be a big focus of their life and interfere with their functioning."
In the past, researchers have often studied the addictive properties of drugs such as tobacco, cocaine, marijuana, heroin and alcohol separately, Hopfer said. But studies such as this s
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