Marijuana’s Effect on Dopamine Key to Mood Changes

Marijuana: Where There’s Smoke, There’s Fire

People who regularly use marijuana have increased odds of experiencing significant symptoms of anxiety and depression, as well as an unusual sensitivity to the impact of emotional stress. This fact also holds true for occasional users of the drug. In a study published in June 2014 in the Proceedings of the National Academy of Sciences, researchers from three U.S. institutions sought to determine why marijuana users have heightened risks for unpleasant mood changes and stress reactions. These researchers concluded that the cause may be marijuana’s ability to alter the brain’s reaction to a key chemical called dopamine.

Marijuana and Mood

Marijuana has a fairly established reputation as a mood-enhancing and pleasure-enhancing drug. However, researchers have long noted that some marijuana consumers can develop unpleasant reactions to the drug, including bouts of paranoia and the hallucinations and delusional thinking normally associated with severe mental illnesses like schizophrenia. In a study published in 2010 in The American Journal of Drug and Alcohol Abuse, a team of Canadian researchers used data gathered from 14,531 Canadian adults to investigate the role of marijuana use in promoting bouts of anxiety and substantially “down” or depressed moods. These researchers concluded that habitual users of the drug are more than 100 percent more likely to experience these problems than people who don’t use marijuana. They also concluded that occasional or infrequent consumers of the drug have a roughly 43 percent higher chance of experiencing anxiety or depressed moods.


Dopamine is one of the brain chemicals that make it possible for nerve cells to “talk” to one another. Among other things, this chemical plays a critical role by helping to control activity levels in a part of the brain known as the pleasure center. Essentially, when dopamine levels rise in this brain area, sensations of pleasure grow stronger. Since humans have a natural preference for pleasurable experiences, they tend to regularly take part in activities that boost their dopamine levels (e.g., eating and having sex).

Dopamine response in the pleasure center is central to the risks for developing physical substance dependence and addiction. This is true because alcohol and the vast majority of mind-altering drugs and medications significantly boost the brain’s dopamine levels. Unfortunately, some consumers of these substances repeatedly use them for their pleasure-producing effects. Eventually, the brain will respond to this repeated substance exposure by changing its basic chemical environment and treating the substance in question as an ongoing requirement for its everyday function. In the case of many substances, this physically dependent state is equivalent with the onset of addiction. In the case of other substances (particularly opioid medications), addiction arises in some of those individuals affected by physical dependence.

Marijuana and Dopamine Changes

In the study published in the Proceedings of the National Academy of Sciences, researchers from the National Institute on Drug Abuse, Brookhaven National Laboratory and the National Institute on Alcohol Abuse and Alcoholism used a dopamine-based experiment involving 48 adults to explore the reasons marijuana use is linked to increased risks for anxiousness and other unpleasant states of mind. Twenty-four of these adults had problems that qualified them for a diagnosis of cannabis/marijuana abuse; the remaining 24 did not use marijuana. During the experiment, the researchers gave the members of both groups doses of methylphenidate, a stimulant-based ADHD medication known for its ability to elevate the brain’s dopamine levels. Next, they asked all of the participants to describe the feelings produced by methylphenidate and used brain scans to measure any dopamine-related brain changes.

At the beginning of the experiment, the study participants affected by marijuana abuse seemed to have just as much capacity to produce dopamine as the participants who didn’t use marijuana. However, after exposure to methylphenidate, the marijuana abusers showed a substantially weaker response to the effects of dopamine. The researchers linked this weakened response to marijuana users’ increased chances of developing anxious, depressed or otherwise unpleasant moods. They also concluded that the marijuana users with the weakest responses to dopamine’s normal effects were the most likely to experience unpleasant mood changes. In turn, the weakest responses to dopamine’s effects were found in those individuals most heavily affected by symptoms of marijuana addiction.

The study’s authors note that their experiment was not designed to determine if dopamine-related problems arise before or after marijuana use. This means that, while marijuana use may trigger these problems, the desire to offset preexisting dopamine-related mood changes may also explain why some people start using marijuana.

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