Chronic Marijuana Use Changes Brain

Posted on June 6th, 2011

Adding to the growing body of evidence that chronic marijuana smoking can have negative effects, a new study shows that heavy marijuana use can lead to brain changes that can affect pleasure, appetite, pain tolerance, and many other psychological and physical functions of the body.

Lead author Jussi Hirvonen, MD, PhD, said that this study showed for the first time that heavy marijuana users have abnormalities of the cannabinoid receptors in the brain. This information may be important for the development of new treatments for marijuana abuse and addiction.

The collaborative study between the National Institute of Mental Heath and the National Institute on Drug Abuse in Bethesda, Maryland, also found that the decreased receptors return to normal levels when marijuana users stop smoking the drug.

The psychoactive chemical in marijuana is THC (delta-9-tetrahydrocannabinol), which binds to several cannabinoid receptors in the brain and throughout the body when marijuana is ingested, producing a “high.” Cannabinoid receptors in the brain are associated with numerous psychological states and actions, including memory, perception of time, pleasure, concentration, coordination, and sensory perception. Other cannabinoid receptors throughout the body are involved in functions of the digestive, cardiovascular, respiratory, and other systems.

There are currently two known types of cannabinoid receptors—CB1, which is involved in functions of the central nervous system, and CB2, which is involved in functions of the immune system and the circulatory system.

In the study, researchers recruited 30 people who smoked marijuana daily, and monitored them at an inpatient facility for about four weeks. After administering a combination of a radioactive fluorine isotope and a neurotransmitter analog that binds with CB1 receptors, the researchers used positron emission tomography (PET) to examine physiological processes in the body.

The researchers found that the number of receptors decreased about 20 percent in chronic marijuana smokers compared to health subject with little exposure to marijuana in their lifetime. The changes correlated with the number of years the subjects had been using marijuana.

Of the 30 participants, 14 underwent a second PET scan after about a month of abstaining from marijuana. The scans showed a significant increase in receptor activity in the areas that had been decreased at the beginning of the study. This suggests that the damage is reversible with abstinence.

The authors note that the findings from this study may help other research examining the adverse effects of chronic marijuana use, as well as in developing treatments for marijuana abuse.

Source: Science Daily, Chronic Marijuana Smoking Affects Brain Chemistry, Molecular Imaging Shows, June 6, 2011

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