What Marijuana Actually Does to Your Brain and Body

What Marijuana Actually Does to Your Brain and Body

Marijuana. Pot. Weed. Whatever you call it, it’s the most popular illegal drug in the world, gaining support for legalisation for both medicinal and recreational purposes. But what does marijuana actually do to us? Let’s take a look at this fascinating drug, its health effects, and potential concerns about using it.

Photos by Nemo, Geralt, 887OS (Shutterstock), trawin, Caveman Chuck Coker, GoToVan, wackystuff

Marijuana Is a Controlled Substance…Lacking in Controlled, Scientific Research

Before we start, we should note that a whole lot more research needs to be done in this area. Although marijuana has been used for centuries as a medicine and as an inebriant (it’s even mentioned in the Old Testament several times as “kaneh-bosem”), we don’t know a great deal about the health effects of using it. That’s because there haven’t been many controlled studies on it, due to the way marijuana is classified by the US federal government.

The Food and Drug Administration classifies marijuana as a Schedule I drug, defined as the most dangerous of all drug schedules, with “no currently accepted medical use and a high potential for abuse.” (Fun fact: heroin, ecstasy and LSD are also Schedule I drugs, but cocaine and meth are considered less dangerous Schedule II drugs.)

As such, to do clinical research with marijuana, you need a license from the DEA and your study approved by the FDA, and to obtain research-grade marijuana, you have to go through the National Institute on Drug Abuse, Popular Science explains. Otherwise, since it’s federally illegal to have marijuana (even in states that have legalised marijuana), researchers working in hospitals, colleges, or other institutions that receive federal funding risk losing their funds to do this research.

There have long been movements to reclassify marijuana and open up the doors for more studies, but, for now, here’s what we do know about marijuana and our health.

What Marijuana Does To Our Brains In The First Couple Of Hours

The video above from ASAP Science explains how marijuana acts on our brains shortly after smoking or ingesting it. Cannabis contains at least 60 types of cannabinoids, chemical compounds that act on receptors throughout our brain. THC, or Tetrahydrocannabinol, is the chemical responsible for most of marijuana’s effects, including the euphoric high. THC resembles another cannabinoid naturally produced in our brains, anandamide, which regulates our mood, sleep, memory and appetite.

Essentially, cannabinoids’ effect on our brains is to keep our neurons firing, magnifying our thoughts and perception and keeping us fixed on them (until another thought takes us on a different tangent). That’s why when you’re high, it’s really not a good time to drive, study for a test, or play sports that require coordination, like tennis or baseball. Like alcohol, caffeine and sugar, cannabinoids also effect the levels of dopamine in our brain, often resulting in a sense of relaxation and euphoria.

Salon explains a few more ways marijuana interacts with our brains, such as impairing our ability to form new memories, and how cannabinoids cause the classic “munchies”.

The effects will depend on the amount taken, as well as how potent the preparation is (common marijuana contains 2-5% THC, while ganja can contain up to 15% THC and hashish oil between 15 and 60% THC). At high doses — and if you don’t follow the 10 commandments of marijuana edible safety — marijuana can produce scary curled-up-on-the-couch-for-hours hallucinatory states.

As with other drugs, marijuana’s effects will also vary by individual. Not all people may find it an enjoyable or relaxing experience; for those who have anxiety or are prone to panic attacks, marijuana could exacerbate their symptoms rather than bring on a sense of calm.

Marijuana Doesn’t Seem to Have a Long-Term Effect on Memory and Concentration


The short-term effects of marijuana are generally felt within a few minutes, peak within 30 minutes, and wear off after about two or three hours. The bigger question is: what happens if we use marijuana more regularly, or are occasional but heavy users? Are there permanent cognitive and other health changes? Do we all turn into The Dude from The Big Lebowski?

Again, we don’t have many rigorous scientific studies on this, much less many longitudinal studies. A 2012 review of available research, however, published in the Journal of Addiction Medicine, finds that the immediate impairments on memory and concentration, at least, aren’t likely permanent:

  • Attention/concentration: Marijuana impairs light users’ attention and concentration but doesn’t appear to affect regular or heavy users within six hours of smoking or ingesting it. In the long run, researchers have found that after 3 weeks or more since last using marijuana, subjects’ attention and concentration return to normal. “In five of seven studies, no attention or concentration impairments were found in subjects who had remained abstinent from 28 days to one year (Lyons et al., 2004; Pope et al., 2001; 2002; 2003; Verdejo-Garcia et al., 2005).” The other two studies found differences in attention and concentration between heavy and non-users after 28 days, but the reviewers note that the disparate findings could be due to measuring different types of processing skills.
  • Working memory: Several studies likewise found no residual or long-term effects on working memory. A 2002 study, for example, tested 77 heavy smokers for days after abstaining from smoking pot. Memory impairment was found for heavy users up to 7 days after using marijuana, but by day 28 their memory test results didn’t differ significantly from control subjects. In other words, even if your memory is affected when you smoke up, after you stop it will likely go back to normal with time.

The Substance Abuse and Mental Health Services Administration (SAMHSA) has a brochure on the possible short- and long-term consequences of using marijuana. It reports that there’s no strong link between frequency of marijuana use and violence or crime, an unclear or weak link between depression and marijuana use, and no clear link between marijuana use and birth defects. Heavy use of marijuana, however, has been linked to increased likelihood of respiratory problems, schizophrenia development (but some studies suggest a genetic predisposition might be involved in these cases), and, for teens increasing pot use, a harder time adjusting to society. We’ll touch on some of these issues below.

Compared To Other Drugs, Marijuana Is Less Addictive And Harmful

Addiction is a very complex topic. It’s possible for people to get addicted to anything that gives us pleasure. While marijuana addiction is real, it is a rarer addiction than other (legal or illegal) substances. Statistics say that 9 percent of people (roughly one out of 10) who use marijuana become dependent on it, compared to 32 percent of tobacco users, 20 percent of cocaine users, and 15 percent of alcohol drinkers.


When it comes to marijuana and other substances, some say what matters most might not be how addictive the substance is but how harmful it might be. Former Surgeon General Jocelyn Elders told CNN she supports legalising marijuana, saying it “is not addictive, not physically addictive anyway”. Time reports:

As Dr. Elders also said on CNN, marijuana is nontoxic. You can fatally overdose on alcohol, heroin or cocaine, but the only way a dose of marijuana will kill you is if someone crushes you under a bale of it.

By and large, marijuana has been shown to be much less dangerous and addictive than other substances — over 100 times safer than alcohol — but that’s not to say it is completely harmless. How marijuana is consumed and prepared can make a big difference on its health effects, for better or worse, as well.

Marijuana Is More Dangerous for Teens


The chances of getting addicted to marijuana increase if you’re a daily user or if you start when you’re a teen. According to the National Institute on Drug Abuse, marijuana addiction goes up to about 17 percent in those who start using young (in their teens) and to 25 to 50 percent among daily users.

Dr. Damon Raskin, internist and Diplomat of the American Board of Addiction Medicine, advises:

Marijuana these days can cause changes in the brain that impair learning, especially in teenagers as their brains have not finished developing. Brains are not fully developed until the age of 25 or 26. Chronic marijuana use can lead to changes in both personality, judgment, and reasoning skills.
Pot damages the heart and lungs, increases the incidence of anxiety, depression and schizophrenia, and it can trigger acute psychotic episodes. Many adults appear to be able to use marijuana with relatively little harm, but the same cannot be said of adolescents, who are about twice as likely as adults to become addicted to marijuana.
Much of the marijuana available today is more potent than it was in the past, so the potential exists for it to have more intense deleterious effects on the user. Medical professionals are seeing more emergency room visits with excessive vomiting, and with adolescents, there is greater risk of psychosis and delirium.

If you’re a parent, this is another reminder to talk to your kids about drugs, especially during those formative years.

Smoking Is Riskier Than Other Methods Of Using


Marijuana is most commonly smoked, but it can be used in vaporisers, turned into a tea, or used as an ingredient in foods as an edible. Oils and tinctures are often made from the cannabis plant as well for medicinal purposes. Of the many ways to use marijuana, smoking seems to have the most harmful side effects. According to the American Lung Association:

Smoke is harmful to lung health. Whether from burning wood, tobacco or marijuana, toxins and carcinogens are released from the combustion of materials. Smoke from marijuana combustion has been shown to contain many of the same toxins, irritants and carcinogens as tobacco smoke.
Beyond just what’s in the smoke alone, marijuana is typically smoked differently than tobacco. Marijuana smokers tend to inhale more deeply and hold their breath longer than cigarette smokers, which leads to a greater exposure per breath to tar.
Secondhand marijuana smoke contains many of the same toxins and carcinogens found in directly inhaled marijuana smoke, in similar amounts if not more.

A review of studies in 2013, however, found mixed evidence linking heavy, long-term marijuana use to pulmonary disease or lung cancer and concluded that there’s definitely a bigger risk for these if you smoke tobacco.

Still, regular users might consider other options besides smoking, such as vaping and edibles. Ata Gonzalez, CEO of G FarmaLabs, says:

Traditional methods (joints, blunts, etc), first off, aren’t the most efficient and certainly aren’t the cleanest ways to do it. These paper-based methods can be harsh on throat and lung tissue over time, potentially introduce the possibility of inhaling mold spores, and can be carcinogenic depending on what the cannabis is rolled in. Vaporizers are a much better option if you’re going to smoke it, not only because it’s much more discreet, but it introduces cannabinoids into the bloodstream as a gas through heat, rather than as smoke due to combustion. Vaping also reduces any possible exposure to harmful toxins/byproducts because the marijuana is never burned.
Conversely, there’s always the edibles option. This method is the most efficient way to get cannabinoids into the system because it’s done through the gastrointestinal tracts instead of the lungs – this also means that absorption is slower and the effects seem like they’re delayed, but that’s because the body has to process THC through the liver. The resulting effect, however, is a much more body-focused “high” that’s optimal for pain relief. Tinctures and tonics are sometimes classified in this subset/consumption category. Finally, we have topical solutions made with cannabis oil (e.g. salves, lotions, ointments, etc.) which are best used as anti-inflammatories and analgesics.

Additionally, if you partake, you’ll ideally want to know where your marijuana came from — who grew it, how they grew it, how they harvested it, and so on. If you don’t know (which is fairly likely in Australia), consider Global Healing Center editor Ben Nettleton’s suggestion to water cure your stuff:

Water curing is basically just soaking your stuff in water and changing the water several times. The water draws out any water soluble impurities. So any leftover fertilizer, pesticides, fungus (recent Smithsonian touched on the prevalence of that), and even innocuous unnecessary compounds like salts and chlorophyll. Pretty much just like giving it a wash. THC is not water soluble so you don’t lose any of what you want.

There Are Many Possible Medical Uses For Marijuana

What Marijuana Actually Does to Your Brain and Body

Finally, there are the potential medical uses of marijuana for a wide variety of conditions. 23 US states and DC have legalised the medical use of marijuana to treat symptoms of cancer, AIDS, arthritis, multiple sclerosis, migraines, epilepsy, nausea and other conditions. 76% of doctors surveyed said they would prescribe marijuana for medicinal purposes. And Procon.org’s analysis of 60 peer-reviewed studies on medical marijuana found 68% of them concluded treatments were positive for the conditions treated.

As with the adverse effects of marijuana, however, the research here is still limited and lacking. CNN’s Dr. Sanjay Gupta, who changed his stance on marijuana to now question marijuana’s categorization as a Schedule I drug, says that of the recent papers on it, the overwhelming majority — about 94% — are designed to investigate the harm while only 6% investigate the benefits of medical marijuana.

So what we’re left with is anecdotal evidence. Greta Carter, marijuana activist, entrepreneur, and founder of a chain of clinics tells me:

What we know is that the VA has clearly identified the benefits of marijuana on post-traumatic stress syndrome. We also know that parents who have struggled daily with children suffering from seizures and movement disorders go to extremes to relocate their families to states that will allow them access to the medicine. We’ve heard from patients with AIDS and cancer who find benefits from cannabis. There are studies outside of the US that actually show tumours being reduced with cannabis treatment. I find it unconscionable that we as a country that have over 500 deaths a year to aspirin, and none to cannabis in its entire history would ever try to stand in the way of this plant being readily available to whomever might seek it.

Opponents of medical marijuana argue that it’s too dangerous to use (though the arguments seem to be mostly associated with the effects of smoking rather than marijuana in general or administered in other ways), that marijuana is addictive, and that legal drugs make marijuana unnecessary.

As ever, “further research is recommended” (isn’t that how all studies conclude?) In the case of marijuana, though, we really do need more.


  • Given the uncertainty over a lot of the effects of marijuana (depite a billion internet level doctors) and the potential side effects it could have and the mythical ones it definitely does not have, there is absolutely a need for controlled, unbiased research to be done. I support this idea completely. I also support the idea of controlled medicinal useage, especially canabid oil for issues such as seizures, cancer use etc.

    • Quite a lot of research has already been done – for example: http://www.ncbi.nlm.nih.gov/pubmed/?term=cannab*+treatment+pain . Albeit mostly in animal or computer models. But there is sufficient human trial evidence to justify the use of cannabinoids, especially as an opiate-sparing analgesic.

      Unfortunately while social stigma and governmental dogma persists, things are unlikely to change quickly. Pity.

      • Which only strengthens the point that more human trials are needed. Computer simulations are nice, but in the end practical experimentation will always trump it due to genetic variation, unexpected results etc. Cannabids are fantastic, but myths do surround them too in regards to their usefulness on both ends of the scale. So, research definitely needs to be done. Personally, I’m of the opinion it should be legalised, but I’m of the opinion education and research into the matter needs to be done first. Like I said, a million internet doctors everywhere will tell us it’s all good, but the simple fact is, we don’t yet know enough, we don’t have to absolute concrete evidence put forward that’s irrefutable, to get where we need to be.

        • My father who is a doctor cured his own mouth cancer with Cannabis oil. Other test results included, disappearance of two specific moles he treated daily for 6 weeks. Better blood pressure, better sleep (which means better recovery)

          This is a man that use to say “weed is for dumb hippies” has been a doctor for 35 years

  • Having seen a friend become steadily more paranoid and erratic after fairly heavy usage I don’t think it’s all quite as fine and dandy as these sorts of articles make it seem. Sure it’s probably not as bad as alcohol or tobacco, but that’s not saying much, both of those are pretty rough on the body as well.

    • I am sorry to hear about your friend, however it must be noted that a lot of people just should not use marijuana. Some people are pre-disposed, both genetically and personality wise, to addictive behaviour and psychosis induced by biochemical inbalances. When comparing them to alcohol and tobacco you forget to mention that cannabis is still illegal in most countries, even by those who use non-psychoactive preparations (like a topical salve or cream for arthritis), while tobacco and alcohol, which have been proven to be neurotoxic, are sold freely (how much does an alcohol service license cost?) and even advertised to teenagers.

      • Regardless of whether he has an addictive personality or not his behavior changed significantly after heavy usage. Don’t get me wrong, controlled use is probably alright, but articles like these tend to skew the drug to a positive outlook because the drugs they compare them to are legal (that is tobacco and alcohol). People somehow think that Marijuana is all sweet just because it’s not as bad as freely available drugs. In my view those freely available drugs are much more dangerous than we are led to believe (although tobacco is certainly starting to reach the reputation it deserves) and Marijuana is still something of an unknown quantity when it comes to long term effects after years of heavy use. I accept that in no way does a single example have any sort of medical relevance (I know someone who’s alergic to capsicum, but he’s obviously an outlier and capsicum is good for most people, or I assume it is until I’m told otherwise buy more intelligent people than me), however people seem to defend Marijuana with a religious fervor that it has not earned in the realm of recreational use.

        I’m not against legalizing or decriminalizing Marijuana, people that want it get it anyway, the only people its status as an illegal drug might prevent from getting it are people who could use it medicinally. Medicinal purposes are obviously very beneficial and I fully support its use in such situations. All that said though I’m very straight edge I don’t smoke anything at all and don’t drink anything worse than the occasional soft drink, so perhaps I exhibit a certain amount of bias.

        • My Uncle and a close family friend both had marijuana induced mental issues. They were very serious and life changing illnesses. I still smoke every day.

          There’s risk but it boils down to this – It’s like anything! Too much isn’t a good idea. If you can control your intake, fine, no worries. Too much water and you drown. Too much air and you pop. Too much booze, too much weed, too much harry… It’s all the same, except for some people a certain substance might make them sick, or they have an allergy to it. Again – This is fairly common place in society. I know people who can’t eat peanuts, so they don’t. Why can’t people who will be killed by weed just not smoke it?

          Each to their own. I don’t see why people who largely abstain should have a say over the people that don’t, and vice versa.

    • Yet there was about 30 adds during the cricket for booze. I too have seen people turn violent, horrible crashes, families torn apart and lives ruined all thanks to the loveable and expectable drink. In moderation its fine with both weed and booze, your friends problem was not weed but himself.

  • Worth pointing out that cocaine and heroin both have accepted medical uses. Cocaine is a potent vasoconstrictor commonly used in ENT procedures to reduce bleeding from the nose. Heroin (diacetylmorphine) is often used in the UK as part of spinal or epidural anaesthesia.

    • You’re not talking street grade cocaine and heroin here though, you’re talking a medicinal level, which is *vastly* different. It’s like comparing ritalin and speed. People will tell you ‘ritalin is pharmaceutical speed’ while technically true, they’re still a world apart…

  • You’re right, Ritalin has a vastly higher number of addicted users when compared to speed…. (Y)

  • “I find it unconscionable that we as a country that have over 500 deaths a year to aspirin, and none to cannabis in its entire history would ever try to stand in the way of this plant being readily available to whomever might seek it.”

    It’s hard to pinpoint the amount of ‘indirect’ deaths caused by weed. e.g. how many people killed themselves / harmed others as a result depression and/or schizophrenia which was caused by prolonged use. I hear the argument above way too much & I’ve even used it myself :/

    It’s a good point about the age. If it were ever made legal, you would certainly want to restrict it to 25+ only.

  • It is shocking to see the lack of knowledge on this issue in Australia. Canada and the United States are on the way to legalization. There are zero legitimate studies that link cannabis use to mental health problems. The APA, American Psychology Association says that it also has zero effect on general health, and no correlation to lung cancer. Legalizing or decriminalizing the drug will keep it out of the hands of teens and children, since licensed providers will ask for proof of age ID, whereas drug dealers don’t care.

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