Marijuana Facts: Daily Pot Smokers Experience Less Pleasure And Reward Than Non-Smokers

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Regular marijuana users are less able to react to dopamine, suggesting their brains may have damaged reward circuitry. Photo courtesy of Shutterstock.

Your brain’s so-called pleasure center is ruled by dopamine, a neurotransmitter that also plays a role in reward-motivated behavior. Although it is a well-known fact that cocaine and alcohol abusers produce far less dopamine than non-addicted people, scientists have not understood whether the same might be true for those who abuse marijuana. Now, a new study from researchers at the National Institute on Drug Abuse (NIDA) shows regular marijuana users to be less able to respond to dopamine, suggesting their brains may have damaged reward circuitry.

Which Comes First?

Among addiction specialists, it is a classic chicken or the egg argument: Are drug abusers born with less dopamine in their brains and is this why they are more inclined to use drugs or does drug over-use cause abusers to feel less pleasure over time? To explore this question, Dr. Nora Volkow and her colleagues at NIDA and New York University designed an experiment using both a personality test and a brain scan. Participants in the study included a group of 24 marijuana abusers — in this case, people who had smoked an average of five joints a day, five days a week, for 10 years — and a second group of 24 participants who did not smoke pot.

Immediately, one difference between the groups was made clear. Heavy marijuana users scored lower for positive emotions and higher for negative emotion on the personality test. Next, participants were given Ritalin (methylphenidate), a stimulant known to increase the amount of dopamine in the brain, while researchers used magnetic resonance imaging (MRI) to scan their brains. What did they observe? Surprisingly, both groups produced equal amounts of extra dopamine after taking Ritalin.

However, while the non-users experienced increased heart rates and reported feeling restless and high, the daily pot smokers felt only a weak response from the drug, suggesting damage in their brain circuitry. All told, the results of both tests suggest heavy users of cannabis may be experiencing less reward from the very things other people find pleasurable. Unfortunately, then, while the study provides some insight, it does not answer whether potheads smoke because their brains are wired in such a way that leads to depression or their depression is a result of frequent cannabis use.

Source: Vokow ND, Wang GJ, Telang F, et al. Decreased dopamine brain reactivity in marijuana abusers is associated with negative emotionality and addiction severity. Proceedings of the National Academy of Sciences. 2014.

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