TUESDAY, June 7 (HealthDay News) -- Imaging scans show that chronic daily use of marijuana can have a detrimental effect on the brain, according to a new report.

In the study, researchers revealed that chronic use of the drug caused a decrease in the number of receptors involved in a wide array of important mental and bodily functions, including concentration, movement coordination, pleasure, pain tolerance, memory and appetite.

Marijuana, also known as cannabis, is abused more than any other illegal drug in America, according to the U.S. National Institute on Drug Abuse. When smoked or ingested, the drug's psychoactive chemical binds to numerous cannabinoid receptors in the brain and throughout the body, which influence a range of mental states and actions. One of two known types of cannabinoid receptors, called CB1, is involved primarily in the central nervous system.

In conducting the study, researchers compared the brains of 30 chronic daily marijuana smokers to non-smokers over the course of roughly four weeks. Using molecular imaging, researchers were able to visualize changes in the participants' brains and found the cannabinoid CB1 receptors of the smokers had decreased by roughly 20 percent compared to the otherwise healthy people with limited lifetime exposure to marijuana.

"With this study, we were able to show for the first time that people who abuse cannabis have abnormalities of the cannabinoid receptors in the brain," lead author Dr. Jussi Hirvonen said in a Society of Nuclear Medicine news release.

The researchers re-scanned 14 of the smokers after one month of abstinence and found a notable increase in receptor activity in areas that were deficient at the beginning of the study. These findings, the investigators concluded, suggest the adverse effects of chronic marijuana use are reversible.

"This information may prove critical for the development of novel treatments for cannabis abuse. Furthermore, this research shows that the decreased receptors in people who abuse cannabis return to normal when they stop smoking the drug," Hirvonen added.

The study, which was a collaboration between the U.S. National Institute of Mental Health and U.S. National Institute on Drug Abuse, was slated for presentation Monday at the annual meeting of the Society of Nuclear Medicine in San Antonio, Texas. Because this study was presented at a medical meeting, the data and conclusions should be viewed as preliminary until published in a peer-reviewed journal.

More information

The U.S. National Institute on Drug Abuse has more on marijuana and its effects on the brain.