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article imageHeavy marijuana use affects dopamine response

By Tim Sandle     Jul 21, 2014 in Health
People who use marijuana heavily appear to have blunted brain responses to dopamine, according to a new study. Dopamine is a chemical messenger associated with pleasant feelings, motivation and reward.
The diminished dopamine response might help explain why some people need to consume what could be regarded as excessive amounts of marijuana. In the brain, dopamine functions as a neurotransmitter — a chemical released by nerve cells to send signals to other nerve cells. The brain includes several distinct dopamine systems, one of which plays a major role in reward-motivated behavior. Most types of reward increase the level of dopamine in the brain, and a variety of addictive drugs increase dopamine neuronal activity. Other brain dopamine systems are involved in motor control and in controlling the release of several other important hormones.
To reach this conclusion, researchers tested brain and body responses of 24 heavy marijuana users. On average, these people smoked nearly five joints a day, five days a week and had been using marijuana for a decade.
Ongoing studies showed that these marijuana users had weaker responses to the stimulant methylphenidate, which is used to treat attention-deficit/hyperactivity disorder, compared with non-users. Furthermore, users reported a less intense “high” from methylphenidate, which increases dopamine in the brain. Bodily responses were also blunted: in users, the stimulant did not affect pulse rate and diastolic blood pressure as strongly.
The main finding was that the dampened dopamine response might actually lead to increased marijuana cravings. In such circumstances "heavy" users need to continue with their high levels of marijuana use due to their bodies biochemical responses.
The research was led by Nora Volkow, director of the National Institute on Drug Abuse in Rockville, Md., U.S., and the findings have been published in the Proceedings of the National Academy of Sciences. The paper is titled “Decreased dopamine brain reactivity in marijuana abusers is associated with negative emotionality and addiction severity.”
More about Marijuana, Dopamine, Hormones, Brain
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