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Cannabis is the most popular illicit(ish) drug in the world, and it’s gaining in popularity as it becomes legal—medicinally or recreationally—in more and more states. But what actually happens in your body when you partake? Let’s take a look at this fascinating drug, its health effects, and potential concerns about using it.


Cannabis 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 cannabis 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 cannabis is classified by the federal government.

The Food and Drug Administration classifies cannabis as a Schedule I drug, 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.) There are two exceptions: FDA-approved drugs made from cannabidiol (CBD) with “no more than 0.1 percent tetrahydrocannabinols” are on schedule V, the same list as codeine-containing cough syrups. And hemp—defined as cannabis plants that contain less than 0.3% THC—is unscheduled thanks to the 2018 Farm Bill.

Because garden-variety cannabis is still on Schedule I, you need a license from the DEA and your study approved by the FDA. To obtain research-grade cannabis, you have to go through the National Institute on Drug Abuse, Popular Science explains. Otherwise, since it’s federally illegal to have cannabis (even in states that have legalized it), 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 cannabis and open up the doors for more studies, but, for now, here’s what we do know about cannabis and our health.


What cannabis does to our brains in the first couple of hours

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 cannabis’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 affect the levels of dopamine in our brain, often resulting in a sense of relaxation and euphoria.


Salon explains a few more ways cannabis 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 cannabis contains 2 to 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 our advice on edible safety—cannabis can produce scary curled-up-on-the-couch-for-hours hallucinatory states.


The Beginner's Guide to Edibles Edibles are tricky business. If you’ve never eaten your way to a high before, you may be a little… Read more

As with other drugs, cannabis’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, cannabis could exacerbate their symptoms rather than bring on a sense of calm.


Cannabis may have a long-term effect on memory and concentration


The short-term effects of cannabis 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 published in the Journal of Addiction Medicine, found that the immediate impairments on memory and concentration aren’t likely permanent. But a 2018 review by Colorado’s public health department concluded that daily users of cannabis can have impaired memory lasting more than a week after quitting. Whether memory or other cognitive problems may last longer than that is still unclear.


Colorado also has a list of statements about the health effects of using cannabis, and a detailed list of how strong the evidence is for each statement. Evidence for most of the mental health effects is “limited” or “mixed,” but a few findings have substantial evidence behind them. They include:

Adolescents and young adults who use cannabis are more likely to develop psychotic symptoms and disorders like schizophrenia

Heavy use of smoked cannabis is associated with chronic lung problems like bronchitis

People who use cannabis can become addicted to it over time

Compared to other drugs, cannabis 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 cannabis 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 cannabis 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 cannabis 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 legalizing cannabis, 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.


Although evidence shows that it’s possible to develop a substance use disorder, and withdrawal symptoms after stopping heavy use, cannabis has still 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 cannabis is consumed and prepared can make a big difference on its health effects, for better or worse, as well.


Cannabis is more dangerous for teens


The chances of getting addicted to cannabis increase if you’re a daily user or if you start when you’re a teen. According to the National Institute on Drug Abuse, cannabis 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


Cannabis is most commonly smoked, but it can be used in vaporizers, 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 cannabis, 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 cannabis 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 want to know where your cannabis came from—who grew it, how they grew it, how they harvested it, and so on. (Soon you’ll be able to buy Willie Nelson’s own brand of weed from his stores!) If you don’t know, however, 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.


We tend to think of cannabis as a hippy all-natural movement, but today legal cannabis is the fastest growing industry in the US—a multi-billion dollar industry—and the purity and quality of the cannabis can matter a great deal to your health and its effect on you.

There are many possible medical uses for cannabis


Finally, there are the potential medical uses of cannabis for a wide variety of conditions. 23 US states and DC have legalized the medical use of cannabis to treat symptoms of cancer, AIDS, arthritis, multiple sclerosis, migraines, epilepsy, nausea, and other conditions. 76% of doctors surveyed said they would prescribe cannabis 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 cannabis, however, the research here is still limited and lacking. CNN’s Dr. Sanjay Gupta, who changed his stance on cannabis to now question cannabis’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 cannabis.


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

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 tumors 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. With those being the extreme situations advocating for cannabis, I am more of the position that cannabis is a part of overall wellness for many. … Having served over 1,000 patients a month (40K to date) walking through my clinics and the average age growing older each year, the stories I’m more accustomed to hearing go like this: The aging population who come in and report that they take over 14 kinds of medications (and some of them are meds to offset the side effects of the other meds), in a year after incorporating cannabis, they come back and are down to 2 or 3 meds and enjoying a better quality of life. From those who have suffered from addiction to pain pills, they use cannabis to manage their pain and are off of their pain meds. The stories going on and on.


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

Health professionals and researchers (and lawmakers) on both sides of the debate continue to argue the pros and cons of cannabis use. As for us regular people, more than half of polled Americans said they were in favor of cannabis (recreational or medical) being sold legally, just like alcohol is.


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

This story was originally published in March 2015 and was updated on August 29, 2019 with current information.

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