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."
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 Behaviors 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.
The active ingredient in marijuana acts in the part of the brain called the hippocampus to alter the way information is processed and how memories are formed. Animal studies have shown that this is particularly true while the brain is still developing.
This is specifically why the legal smoking age is 21 in the states that have legalized it.
This blockage of memory formation can cause cognitive impairment in adulthood if use happens during adolescence, at least in rats. It can also quicken age-related brain cell loss, though some studies have suggested that marijuana may be able to slow the progression of Alzheimer's disease.
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.
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.
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.
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.
Marijuana users who have taken large doses of the drug may experience acute psychosis, which includes hallucinations, delusions, and a loss of the sense of personal identity.
There is also possible link between cannabis use and psychotic episodes, but it's impossible to say if pot smoking puts people ar risk of a psychotic episode, or if people at risk of a psychotic episode are more likely to use pot.
Even more complicated? While THC seems to induces acute psychotic effects and cognitive impairment, CBD may have some antipsychotic properties, a new paper suggests. This could even explain or temper the link between cannabis use and schizophrenia and psychosis mentioned above.
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.
There are five stages of sleep, which get progressively deeper as the night goes on. The first four stages are called rapid eye movement, or REM. THC, the main active chemical in marijuana, has been shown to interrupt the later phases of REM sleep, the point during the night that is most crucial to making the body feel re-energized when you wake up.
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.
The traditional red eyes of a marijuana user — Visine anyone? — come from blood vessels expanding in the eye.
One uncomfortable effect of smoking weed is dry mouth or thirst.
The common side-effect, equivalent to the feeling of having a bunch of cotton balls shoved in your mouth, is not just the result of inhaling hot smoke. It turns out cannabinoids receptors are located where our saliva is produced. When these receptors are activated by cannabis use, they inhibit the production of saliva.
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.
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 analyzed 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.
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.
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.
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.
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.
Marijuana may be able to slow the progression of Alzheimer's disease, a study led by Kim Janda of the Scripps Research Institute suggests.
The 2006 study, published in the journal Molecular Pharmaceutics, found that THC, the active chemical in marijuana, slows the formation of amyloid plaques by blocking the enzyme in the brain that makes them. These plaques seem to be what kill brain cells and seem to cause the effects of Alzheimer's.
A synthetic mixture of CBD and THC seem to preseve memory in a mouse model of Alzheimer's disease. Another study suggested that in population-based studies, a THC-based persciption drug called dronabinol was able to reduce behavioral disturbances in dementia patients.
One chemical found in marijuana, called cannabidiol, prevents cancer from spreading, researchers at California Pacific Medical Center in San Francisco reported in 2007.
Cannabidiol stops cancer by turning off a gene called Id-1, the study, published in the journal Molecular Cancer Therapeutics, found. Cancer cells make more copies of this gene than non-cancerous cells, and it helps them spread through the body.
The researchers studied breast cancer cells in the lab that had high expression levels of Id-1 and treated them with cannabidiol. After treatment the cells had decreased Id-1 expression and were less aggressive spreaders. This hasn't been studied in cancer patients, though, and there's no way to be sure that enough of the CBD would get into your body to actually mimic the study.
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.
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.
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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