Chronic Pot Use Can Make You Depressed, Study Says
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Contrary to popular stereotypes, marijuana dampens the brain’s reaction to dopamine, according to a study published on Monday in the journal Proceedings of the National Academy of Sciences.
A team led by Nora Volkow from the U.S. National Institute on Drug Abuse studied the brains of 24 marijuana abusers and how they reacted to methylphenidate, also known by its brand name Ritalin, a stimulant used to treat ADHD and narcolepsy. Marijuana abusers in the study smoked on average five joints a day, five days a week for a decade.
The research team used personality tests and brain imaging to monitor how the marijuana abusers react to methylphenidate, which elevates dopamine. They found that both groups produced just as much extra dopamine after taking the stimulant. However, the marijuana abusers had significantly dampened behavioral, cardiovascular, and brain responses to methylphenidate compared with the control group.
The marijuana abusers’ heart rate and blood pressure were lower in comparison, and they reported feeling restlessness and anxiety. The researchers concluded that marijuana not only dampens the brain's dopamine reaction to stimulants, but also influences the area of the brain involved in reward processing. The marijuana abusers’ weaker physical response to the same amount of dopamine suggests the reward circuitry in their brains is damaged.
The study “suggests that cannabis users may experience less reward from things others generally find pleasurable and, contrary to popular stereotypes, that they generally feel more irritable, stressed, and just plain crummy,” according to neuropsychologist at Florida International University Raul Gonzalez, who was not involved with the research.
Despite the study’s unexpected findings, many questions remain unanswered. “[The study] probably tells you more about cannabis dependence than about recreational use,” said Paul Stokes, a psychiatrist at Imperial College London, also not involved in the research.