To understand what marijuana does to a user in the long run, it’s necessary to look at how the drug works in the brain. Marijuana is as effective as it is because its active chemical compound (tetrahydrocannabinol, or THC) mimics substances called endocannabinoids that the human body produces on its own. In the brain, endocannabinoids work by controlling the production of neurotransmitters (chemical substances that facilitate communication between the brain and the central nervous system). In the rest of the body, endocannabinoids relax muscles, reduce inflammation, protect damaged tissue, and regulate appetite and metabolism, among many other functions.
Because endocannabinoids are so important, the brain has readymade receptors for them. Since the THC in cannabis mimics natural endocannabinoids, marijuana is unique among other drugs in that regard. The same physiological effects that arise from the normal application of endocannabinoids are triggered with the use of marijuana, especially in the brain. This is why smokers experience memory issues, augmented levels of pain, and alterations to emotion, pleasure, and movement control.
The memory issues come from the way marijuana hits the hippocampus, the region of the brain that regulates short-term memory. The effect of cannabis temporarily prevents the brain from developing new memories and learning new things, which is a form of short-term memory.
Researchers who published their findings in the Molecular Psychiatry journal discovered that heavy cannabis users are at risk for developing false memories, even if those users had gone without smoking pot for over a month.
Such a finding is one of a number that suggests people who were regular marijuana smokers in their teenage years are more likely to have memory problems as adults. One such study was published in the Hippocampus journal, which found that teenagers who smoked pot every day for three years had “abnormally shaped” hippocampal regions when they reached their early 20s. Those individuals “performed around 18 percent worse in long-term memory tests,” compared to other test subjects who had never smoked marijuana.
Another study published in JAMA Internal Medicine noted much the same thing, with researchers surprised that there was “such a consistent association with verbal memory for chronic exposure to marijuana,” even when other factors (like cigarettes and alcohol) were accounted for. As past years of marijuana use went up, verbal memory scores went down; expressed numerically, 50 percent of pot smokers tended to remember one fewer word from a list of 15 words. One of the study’s authors worried that “this transient effect” could damage how the brain processes information and how that information is recalled later.
There is much more research that suggests people who regularly smoke marijuana (on a daily basis) for a number of years struggle with cognitive tasks more than those who either do not smoke cannabis or who do so infrequently and/or for shorter periods of time. According to one researcher speaking to Reuters Health, people who smoke marijuana occasionally and then give up the habit (“as most cannabis users do”) have a lower risk of developing problems with their thinking power and memory. Nonetheless, he warned that cannabis is still a drug, and all drugs have some level of harm to them.
Aside from memory, other research has looked at the long-term effects of marijuana on dopamine. Production of the neurotransmitter that regulates the pleasure and reward centers of the brain can be compromised if the marijuana use is heavy, according to an article in Molecular Psychiatry found. People who smoked a lot of marijuana tested positive for lower dopamine release in the region of the brain that also controls attention and impulsive behavior. Participants in this study tended to start smoking pot around the age of 16 and became dependent on the substance by 20. In the month before the study was conducted, nearly all users reported smoking marijuana on a daily basis.
A former president of the American Psychiatric Association commented on the study, saying that there is a growing body of evidence that shows that youth use of cannabis develops into problems in adulthood.
Many of those problems manifest physically, not just psychologically. Healthline explains that since marijuana smoke consists of a number of toxic chemicals (such as ammonia and hydrogen cyanide), long-term exposure to smoking can damage the bronchial passages and the lungs. Regular pot smokers are more likely to have persistent coughs, have some trouble breathing, and produce excess phlegm and mucus from their throats. In fact, the Journal of General Internal Medicine writes that what marijuana smoking does to respiratory health “has some significant similarities to that of tobacco smoking.”
Out of the respiratory system, THC (the active compound in cannabis) exits the lungs and enters the bloodstream, where it moves throughout the body. The National Institute on Drug Abuse cautions that the chemical can increase the heart rate by as many as 50 beats per minute, which can last as long as three hours. Smokers who have heart disease could be at a greater risk of heart attack. Research from the Journal of the American Heart Association suggests that regular marijuana use can not only contribute to the possibility of a heart attack, but also to heart rhythm disorders and stroke, even in young people who have no other risk factors for heart disease.
The point is echoed by the American College of Cardiology, which notes that marijuana causes irregular heart rates and increases the risk of an acute coronary syndrome, which refers to any number of conditions that can be brought on by the sudden interruption of the blood flow to the heart. As a result of this, users who are susceptible to conditions of the heart are taking a serious risk when they smoke marijuana. “Marijuana’s use,” writes the American College of Cardiology, “may be associated with increased mortality in patients with a history of myocardial infarctions (heart attacks).”
One of the more distressing risks of long-term effects of marijuana consumption is found in women who are pregnant. Health Canada explains that smoking pot during pregnancy “has been associated with long-lasting harm to the exposed child’s memory.” In addition to potential damage done in utero, cannabis toxins are also carried in breast milk and can be passed to the infant during breastfeeding. The U.S. government’s National Institute of Child Health and Development also advises against the consumption of recreational drugs before pregnancy and during breastfeeding.
Research has been spotty on how much risk cannabis poses to unborn and nursing babies, but an assistant professor of maternal fetal medicine at Washington University nonetheless cautions that “any foreign substance that doesn’t benefit maternal or fetal health should be avoided,” and that women who want to become pregnant or who are already pregnant play it safe when it comes to using marijuana.
Listing “What 20 Years of Research Has Taught Us About The Chronic Effects of Marijuana,” Forbes details some other problems that arise with the long-term consumption of cannabis, including:
Marijuana has a complicated relationship with sexual libido and function. On the one hand, researchers in the journal of Archives of Sexual Behavior noted that “the illegality of marijuana actually facilitated” the sexual exploits of study participants, with many people using the thrill of the illegal activity (where the purchase and use of cannabis are taboo) to augment their sexual desires and behaviors.
However, animal studies have found that marijuana inhibits the receptors in the erectile tissue of the (animal) penis, according to a study in the Journal of Sexual Medicine, suggesting that cannabis consumption before sex does more to limit sexual function than it does to help it.
Even as some research has suggested that long-term marijuana use carries a minimal risk of physical consequences, such as that published in JAMA, scientists still urge caution. “Buyer beware,” write doctors in Massachusetts, saying that there are not as many health risks associated with heavy marijuana use as previously thought, but health risks exist nonetheless.
The sentiment is shared by some smokers themselves. Writing in Vice magazine, one user noted that most of the heavy smokers he knows get high on a regular basis without the stereotypical feelings of laziness or paranoia. But, he warns, “this isn’t always the case.” As time goes on, and as their habit persists, they tend to experience greater levels of social anxiety and general anxiousness after they smoke compared to when they go without. Some went so far as to note that long-term weed use even changed their personalities, making them less outgoing and socially engaged.
One negative effect the JAMA scientists noticed was that people who smoked pot for a long time tended to have worse periodontal (gum) health than others, which in some cases led to the development of gum disease. Those same scientists pointed out that “marijuana use is associated with increased risk of psychotic illness, IQ decline, and downward socioeconomic mobility,” and that even though this particular study did not find much by way of damage to physical health, “heavy recreational cannabis use does have some adverse consequences.”
Aside from effects on the brain and body, what else can the long-term consumption of marijuana do? The Clinical Psychological Science journal looked at what cannabis did to midlife economic and social status, and wrote that regular cannabis users experienced downward social mobility and financial difficulties, like struggling with debt and cash flow.
Researching the full effects of the long-term dangers of marijuana on the brain and body is difficult because cannabis is still a Schedule I drug in the United States, which places “significant restrictions” on the scientific examination and investigation that can be done with the substance. Nonetheless, even as the legal and political trend is to move marijuana into the mainstream, the medical community has sounded alarm bells over what years-long exposure to cannabis can do. While doctors were surprised at the JAMA Psychiatry study (with one saying, “You need to be willing to change your mind on these issues.”), the consensus remains clear: Unchecked, long-term marijuana smoking damages the brain’s capacity for memory and cognitive tasks, and increases the risk for the development of a number of health problems later in life.