Happy 4/20! Here's what happens to your body and brain when you smoke marijuana

It’s April 20. For those not in the know, “4/20” is the unofficial holiday that pot smokers and marijuana legalization activists around the world celebrate by lighting up.

The plant, best-known for its “feel-good” effects and touted for its uses for multiple diseases, can also damage our bodies and minds.

The high you get from marijuana mostly comes from a chemical called Tetrahydrocannabinol, also known as THC, which is found in varying amounts in different strains of cannabis.

Another important compound is cannabidiol, CBD, which is thought to cause many of the medical effects of marijuana. There are also more than 70 other chemicals in marijuana that could also cause effects on the brain and body that haven’t been well studied.

Most of THC’s effects happen in the brain, where the chemicals in the plant interact with receptors on brain cells called cannabinoid receptors. Our bodies actually make chemicals very similar to THC, which are used in normal brain function and development. THC co-opts these natural pathways to produce most of its effects, which are varied and depend on how much and how often someone uses pot.

Marijuana makes us feel good.

When THC hits brain cells, it causes them to release dopamine, a feel-good brain chemical. This is a part of the brain's reward system, which makes you feel good when you do things that ensure the survival of yourself and your offspring. These things include eating and having sex.

When over-excited by drugs, the reward system creates feelings of euphoria.

But too much of a good thing can become a problem, as the more often you trigger this feeling, the less you can feel happiness for other 'rewarding' experiences. It takes a lot of pot use to get to this point, though.

In a recent study of people who had smoked nearly five joints a day, five days a week, for more than a decade, researchers saw that heavy pot smokers had weaker responses to the stimulant methylphenidate, which is used to treat attention-deficit/hyperactivity disorder, than nonusers. The stimulant gave them a less intense 'high.'

It can be addictive.

A man smokes marijuana during a demonstration in support of the legalization of marijuana in Buenos Aires, December 4, 2014.

Because of those feel-good effects, extended, heavy use of marijuana can be addictive or cause dependence. That doesn't mean anyone who tries marijuana will become addicted -- most causal pot users most likely aren't -- but there are some factors that could increase the likelihood of addiction.

New studies have found that pot can be more addictive when used in combination with nicotine (in the form of blunts) or when used through a vaporizer or other means, which may be more potent than smoking. According to researchers, this could mean that physiological effects of vaporized marijuana extracts could be very different from those of smoked marijuana, since the vaporized marijuana contains mostly THC, the main psychoactive compound.

A study in the journal Addictive Behaviours researchers found that compared to marijuana smokers, users who ingest hash oil using a wax, called 'dabbing,' or by inhaling marijuana oil using a 'vape pen,' may more rapidly develop tolerance and may also have a greater risk of withdrawal -- two signs of addiction.

THC messes with your balance.

THC messes with brain areas called the cerebellum and basal ganglia, which regulate balance, posture, coordination, and reaction time.

When these brain areas are disturbed, the user has a harder time walking and talking correctly, becoming quite clumsy.

Cannabis use may increase the risk of depression.

Although there is no conclusive evidence that marijuana makes users depressed (it's just as likely that people who are depressed use pot), one recent study from the Netherlands found that smoking cannabis increases the risk of depression for young people who have a genetic vulnerability to the mental illness.

In the long-term, smoking marijuana increased depressive symptoms in subjects with a special serotonin gene responsible for increased risk of depression.

Intense anxiety, fear, distrust, or panic are common side effects.

Somewhere between 20% and 30% of recreational marijuana users react with intense anxiety after taking the drug, making it one of the most commonly reported side effects.

A recent study suggested that this could be about specific ratios of THC and CBD in a given strain, since these two chemicals contribute different effects. Some of those effects are giddy, excited highs while others are more mellow -- and some anxiety-inducing.

But it may decrease anxiety too, provided people don't consume too much.

Medical marijuana users claim that the drug helps relieve pain and suppress nausea -- the two main reasons it's often used to relieve the side effects of chemotherapy.

In 2010, researchers at Harvard Medical School suggested that that these benefits may actually be from reduced anxiety, which would improve the smoker's mood and act as a sedative in low doses. Beware, though, higher doses may increase anxiety and make you paranoid.

Audio and visual hallucinations are common.

Along with actual psychosis, cannabis users can also have audio and visual hallucinations from the effects on the brain areas that process what we see and hear.

These audio hallucinations include 'looping' sounds, where one particular sound (that is usually one syllable in duration) will repeat over and over again until it is either replaced by a different sound or the effects of THC begin to wear off.

Inhaling marijuana causes your heart rate to increase.

A London tourist smoking pot in Amsterdam.

Within a few minutes of inhaling marijuana, your heart rate increases, sometimes by 20 to 50 beats per minute (normal is 70 to 80 beats per minute). In some cases, like when taking other drugs with marijuana, heart rate can double.

This heart rate increase usually subsides relatively quickly, in about 20 minutes. In some cases of acute cannabis intoxication this could have cause fatal cardiovascular complications that ended in death.

You may get the munchies.

After marijuana intake, most people feel the need to eat. And eat a lot. The drug increases food enjoyment and interest in food, increasing appetite. This is thought to be caused by the THC interacting with the cannabinoid receptors in a brain area called the hypothalamus.

Interestingly, a link has been drawn between milk products and cannabinoids. Some researchers think that these cannabinoids in milk play an important role in infant survival, because they stimulate the child's appetite and cause them to eat more and suckle, which could be why THC has a similar effect in adults.

According to a recent study in mice published in the journal Nature Neuroscience, marijuana may effectively flip a circuit in the brain that is normally responsible for quelling the appetite, triggering us to eat instead,.

It all comes down to a special group of cells in the brain which normally get activated, or switched on, after we've eaten a big meal to tell us we've had enough. In the brain, though, the psychoactive ingredient in weed appears to activate just one component of those appetite-suppressing cells, known as pro-opiomelanocortin neurons, making us hungry instead.

But it keeps you skinny and helps your metabolism.

A study published in the American Journal Of Medicine on April 15, 2013 suggested that pot smokers are skinnier than the average person and have healthier metabolism and reaction to sugars, even though they do end up eating more calories because of the munchies.

The study analysed data from more than 4,500 adult Americans -- 579 of whom were current marijuana smokers, meaning they had smoked in the last month. About 2,000 had used marijuana in the past, while another 2,000 had never used the drug.

They studied their body's response to eating sugars: their levels of the hormone insulin and their blood sugar levels while they hadn't eaten in nine hours, and also after eating sugar.

Not only are pot users skinnier, but their body has a healthier response to sugar.

It's better for your lungs than tobacco.

According to a study published in Journal of the American Medical Association in January, marijuana does not impair lung function and can even increase lung capacity.

Researchers looking for risk factors of heart disease tested the lung function of 5115 young adults over the course of 20 years. Tobacco smokers lost lung function over time, but pot users actually showed an increase in lung capacity.

The increased lung capacity may due to taking a deep breaths while inhaling the drug, since any time you are inhaling burning smoke, you are taking in particulates into your lungs.

But here's the good news, it looks like how you take in the drug can also impact how it affects your lungs. A 2004 study in the Journal of Cannabis Therapeutics found that vaporized marijuana contained little other than cannabinoids, and a 2007 study found vaporizer users inhaled fewer toxic compounds and carbon monoxide.

It may help control epileptic seizures.

Marijuana use can prevent epileptic seizures in lab animals, a 2003 study showed. though there haven't been any actual studies of humans of the drug as a treatment for epilepsy, there are plenty of case studies and anecdotal examples of cannabis treating seizures in the news lately.

That being said, these aren't rigorous studies conducted by doctors, so we can't say for sure if there is a link between marijuana and seizures, or what in the pot may be helping control the disorders for those who swear by it.

The Epilepsy Foundation supports the development of cannabis-based drugs under the FDA process, and hopefully more research can isolate how these chemicals work in the brain, especially in the brains of patients and children with seizure disorders.

It relieves arthritis discomfort.

Marijuana alleviates pain, reduces inflammation, and promotes sleep, which may help relieve pain and discomfort for people with rheumatoid arthritis, researchers announced in 2011.

Researchers from rheumatology units at several hospitals gave their patients, sativex, a cannabinoid-based pain-relieving medicine. After a two week period, people on Sativex had a significant reduction in pain and improved sleep quality compared to placebo users.

Marijuana treats inflammatory bowel diseases.

Patients with inflammatory bowel diseases like Crohn's disease and ulcerative colitis could benefit from marijuana use, studies suggest.

University of Nottingham researchers found in 2010 that chemicals in marijuana, including THC and cannabidiol, interact with cells in the body that play an important role in gut function and immune responses. The study was published in the Journal of Pharmacology and Experimental Therapeutics.

THC-like compounds made by the body increase the permeability of the intestines, allowing bacteria in. The plant-derived cannabinoids in marijuana block these body-cannabinoids, preventing this permeability and making the intestinal cells bond together tighter.

It can reduce your need for painkillers.

There seems to be a link between legal marijuana and opioid use -- heroin and prescription painkillers like oxycontin. In the 23 U.S. states where medical marijuana is legal, deaths from opioid overdoses decreased by almost 25% between 1999 and 2010, according to a report from 2014.

It could be that instead of getting hooked on painkillers, patients who could use medical marijuana turned to the more 'natural' pain reliever. The study showed that patients using medical marijuana also used prescription painkillers, but they were using the drugs less frequently, thereby reducing the likelihood of overdose.

Pot use is linked to physical changes in the brain.

The orbitofrontal cortex.

In a recent study, scientists used a combination of MRI-based brain scans to get one of the first comprehensive, three-dimensional pictures of the brains of adults who have smoked weed at least four times a week, often multiple times a day, for years.

A critical part of the brain that helps us process emotions and make decisions appeared smaller than in the brains of the nonsmoker. But oddly, the connections passing through that region of the brain were stronger and thicker.

So does smoking weed every day for a decade shrink your brain and make you dumber? Not quite.

The regular smokers did have lower IQ scores overall when compared to the people who didn't smoke, but there's no way to know yet whether or how that might be linked to smaller orbitofrontal cortices or marijuana use in general.

'We cannot honestly say that that is what's happening here,' Francesca Filbey, the lead study author, told Business Insider. It could be that other factors impact brain size and shape, and those factors could be what leads to pot smoking, instead of the other other way around.

It can make you perform better at sports.

Researchers say that marijuana has an anti-inflammatory effect and that the chemical compounds that come from weed might mimic the body's natural endorphins, which could help increase our pain threshold like a natural runner's high and make it easier to push through a tough workout.

So there's evidence that pot can help people deal with pain and inflammation while decreasing anxiety and improving mood, but it also has potentially risky motor-control side effects that could lead to an accident, especially in a sport where a wrong turn (like mountain biking or skiing) could be disastrous.

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