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While marijuana use is becoming less of a tabu, in light of medical legalization in places like Colorado, California or Uruguay, the same can’t be said about marijuana research. A while ago, I mentioned how only 6% of marijuana research studies the benefits, which is completely biased and absurd to begin with, considering policymakers have legalized the herb in many states. What’s troubling me is that we’re not talking about some new chemical or anything. We’re talking about a natural herb that’s been ingested for thousands of years and that’s currently being used by millions of people all over the world, yet we know very little about the potential beneficial or adverse effects to health. For instance, it might just be case that heavy marijuana use could rewire the way dopamine is being used in the brain’s pleasure center, leaving users feeling crummy and miserable. It might also be the case marijuana use could cure cancer, but we’re not seeing enough research done because scientists have too pass through four regulatory agencies, including the DEA, to study anything of the like.

(/rant) Back to heavy pot smokers and dopamine, researchers at the National Institute on Drug Abuse in Bethesda, Maryland wanted to see how the drug affects dopamine production and distribution in the brain. The neurotransmitter is triggered when undertaking pleasurable activities like eating, sex or taking some drugs. Some psychoactive substances, however, come with a big downer as a result of abuse. Alcoholics and cocaine addicts, for instance, are known to have serious trouble producing as much dopamine as non-users, which in turn makes them depressed and lifeless.

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Some studies have hinted that marijuana might also hijack the dopamine system, so Nora Volkow, the director of the National Institute on Drug Abuse in Bethesda, and her team decided to investigate further. The researchers gave methylphenidate, commonly known as Ritalin – a substance that increases the amount of dopamine found in the brain – to 24 marijuana abusers (who had smoked a median of about five joints a day, 5 days a week, for 10 years) and 24 controls.

Brain imaging showed that both controls and abusers produced roughly just as much extra dopamine, but what significantly differed was the witnessed effects. While the controls had higher heart rates, became more anxious and, basically, got high, the marijuana abusers didn’t report anything different happening with their bodies or mood – it just didn’t kick in for them!

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This lack of response has prompted the researchers to believe the reward circuitry in the brains of heavy marijuana users might be damaged. Apparently, abusers and non-users produce just as much dopamine, but the way the neurotransmitter gets used differs which makes the whole situation really tricky. According to the people involved in the study, this disconnection might cause heavy marijuana smokers trouble finding pleasure in other-wise enjoyable, common activities. Ironically, heavy marijuana smokers might become stressed, irritable or depressed. And yet, it’s unclear from the study whether heavy marijuana users smoke a lot because they have a poor dopamine distribution network or their reward system is screwed because they smoke a lot. Not being able to tease out cause and effect “is a limitation in a study like this one,” Volkow says.

The report was published in the Proceedings of the National Academy of Sciences.