What marijuana does to your body and brain

Marijuana's official designation as a Schedule 1 drug means it is pretty tough to study

Researchers believe it is the first time scientists have proven it is possible to identify chronic marijuana use from brain activity following visible cues (Getty)

Marijuana's official designation as a Schedule 1 drug — something with "no accepted medical use" — means it is pretty tough to study.

Yet numerous anecdotal reports as well as some studies have linked marijuana with several purported health benefits, from pain relief to helping with certain forms of epilepsy.

Still, experts say more rigorous scientific analyses are needed. Use of marijuana, a psychoactive drug, can come with risks, especially in people who may be prone to addiction or mental illness. Take a look at how marijuana can affect your brain and body:

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Marijuana can make us feel good.

(SHAWN THEW/AFP/Getty Images (SHAWN THEW/AFP/Getty Images)

One of weed's active ingredients, called tetrahydrocannabinol, or THC, interacts with our brain's reward system, the part that has been primed to respond to things that make us feel good, like eating and sex.

When overexcited by drugs, the reward system creates feelings of euphoria. This is also why some studies have suggested that excessive use can be a problem in some people: The more often you trigger that euphoria, the less you may feel for other rewarding experiences.

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It can make your heart race.

Within a few minutes of inhaling marijuana, your heart rate can increase by 20 to 50 beats a minute. This can last anywhere from 20 minutes to three hours, according to the National Institute on Drug Abuse.

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Weed may help relieve some types of pain...

(Getty Images (Getty Images)

Pot also contains cannabidiol, and this chemical — while not responsible for getting you high — is thought to be responsible for many of marijuana's therapeutic effects, from pain relief to a potential treatment for certain kinds of childhood epilepsy.

Still, while we have a lot of anecdotal reports from individual users who claim that marijuana has helped relieve their symptoms, few controlled scientific studies exist to support these claims, since the drug is still illegal in most of the US.

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... like the discomfort of arthritis...

(Getty (Getty)

Nevertheless, some small studies support the idea that marijuana can have beneficial results for certain ailments. One of the ways scientists think it may help with pain is by reducing inflammation, a component of painful illnesses like rheumatoid arthritis.

A preliminary 2005 study of 58 patients with RA, roughly half of whom were given a placebo and roughly half of whom were given a cannabis-based medicine called Sativex, found "statistically significant improvements in pain on movement, pain at rest ... and quality of sleep" for patients on Sativex.

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... or the pain of inflammatory bowel disease.

Some people with inflammatory bowel diseases like Crohn's and ulcerative colitis could also benefit from marijuana use, studies suggest. But most researchers still say more studies are needed.

A 2014 paper, for example, describes two studies of chronic Chron's patients in which half were given the drug and half were given a placebo. The first study showed a decrease in symptoms in 10 of 11 subjects on cannabis, compared with just four of 10 on the placebo. But when they did a follow-up study using low-dose cannabidiol they saw no effect in the patients.

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Marijuana may also be helpful in controlling epileptic seizures.

Teen marijuana use has fallen at a time when four states and the District of Columbia have legalised the drug (Getty Images)

A drug called Epidiolex, which contains cannabidiol (the marijuana component mentioned above in slide No. 3) may be on its way to becoming the first of its kind to win approval from the Food and Drug Administration for the treatment of rare forms of childhood epilepsy. The company that makes it, GW Pharma, is exploring cannabidiol for its potential use in people with Dravet syndrome and Lennox-Gastaut syndrome, a rare form of childhood-onset epilepsy that is associated with multiple types of seizures.

In March the company came out with phase-three trial data that showed positive results of the drug.

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But it can also mess with our sense of balance.

It may throw off your balance, as it influences activity in the cerebellum and basal ganglia, two brain areas that help regulate balance, coordination, reaction time, and posture.

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And it can distort our sense of time.

A man shops at a marijuana dispensary in Portland, Oregon, one of four US states which permit recreational use of the drug (Josh Edelson/AFP/Getty Images)

Feeling as if time is sped up or slowed down is one of the most commonly reported effects of using marijuana. A 2012 paper sought to draw some more solid conclusions from some of the studies on those anecdotal reports, but it was unable to do so.

"Even though 70% of time estimation studies report over-estimation, the findings of time production and time reproduction studies remain inconclusive."

In 1998 study focusing on the brains of volunteers using magnetic resonance imaging, the authors noted that many had altered blood flow to the cerebellum, which most likely plays a role in our sense of time.

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Weed can also turn your eyes red.

Since weed makes blood vessels expand, it can give you red eyes.

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And you'll probably get the munchies.

A case of the munchies is no figment of the imagination — both casual and heavy marijuana users tend to overeat when they smoke.

Marijuana may effectively flip a circuit in the brain that is normally responsible for quelling the appetite, triggering us to eat instead, according to a recent study in mice.

It all comes down to a special group of cells in the brain that are normally activated after we have eaten a big meal to tell us we've had enough. The psychoactive ingredient in weed appears to activate just one component of those appetite-suppressing cells, making us feel hungry rather than satisfied.

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Marijuana may also interfere with how we form memories.

A woman smokes marijuana during a rally in front of the Supreme Court of Justice in Mexico City (AFP/Getty)

It can mess with your memory by changing the way your brain processes information, but scientists still aren't sure exactly how this happens. Still, several studies suggest that weed interferes with short-term memory, and researchers tend to see more of these effects in inexperienced or infrequent users than in heavy, frequent users.

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And in some people, weed could increase the risk of depression.

Scientists can't say for sure whether marijuana causes depression or whether depressed people are simply more likely to smoke. But one study from the Netherlands suggests that smoking weed seemed to raise the risk of depression for young people who already have a special serotonin gene that could make them more vulnerable to depression.

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Regular use is linked with some specific brain changes — but scientists can't say for sure whether one causes the other.

In a recent study, scientists used a combination of MRI-based brain scans to get a better picture of the brains of adults who have smoked weed at least four times a week for years.

Compared with people who rarely or never used, the long-term users tended to have a smaller orbitofrontal cortex, a brain region critical for processing emotions and making decisions. But they also had stronger cross-brain connections, which scientists think smokers may develop to compensate.

Still, the study doesn't show that pot smoking caused certain regions of the brain to shrink; other studies suggest that having a smaller orbitofrontal cortex in the first place could make someone more likely to start smoking.

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