Marijuana's long-term effects on health: Facts & myths


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Mary Jane stole some of the show from Barack Obama and Mitt Romney this past Election Day, with three states voting on whether or not to legalize marijuana for medical use, and three more deciding whether or not to legalize recreational marijuana. The results were arguably as exciting as the presidential win, with Massachusetts passing a referendum for the drug’s medical use — making it the 18th state to legalize it, in addition to Washington D.C. — and Colorado and Washington passing ones for its recreational use.

With the increasing acceptance of pot comes important questions about its effects on our health. Marijuana — the dried flowers, leaves and stems of the Cannabis sativa plant — is the most commonly used illegal drug in the United States. Recreational users smoke it, vaporize and inhale it, or add it to food or tea to benefit from the psychological effects caused by its active ingredient, delta-9-tetrahydrocannabinol, or THC. Medically, AIDS and chemotherapy patients are prescribed the drug as a way to stimulate their appetite, which is decreased due to the disease and therapy, respectively, and is increased by THC’s side effect of what you know as “the munchies.”

In the short term, smoking pot causes rapid heart rate, increased blood pressure, increased rate of breathing, red eyes, dry mouth, increased appetite and slowed reaction time, according to WebMD. Psychologically, the drug distorts users’ sense of time and sometimes causes paranoia, magical or “random” thinking, short-term memory loss, anxiety and depression. These effects dissipate after three to four hours, but since THC is fat-soluble, it stays in the lungs and brain tissue for up to three weeks.

Pot’s effect on our long-term health is highly debated among experts, and researchers have a long way to go to establish conclusive evidence about many of its possible side effects. But here’s what the current research is saying:



The American Lung Association states that marijuana smoke contains a higher amount of carcinogens than tobacco smoke, and most experts agree that weed smokers typically inhale more smoke for a longer period of time, which leaves more than four times as much tar in the lungs as cigarettes do. However, this is somewhat leveled off by the fact that most marijuana smokers aren’t smoking as frequently as most cigarette smokers and smoke fewer joints.

There is currently not enough scientific evidence to link marijuana use to lung cancer, but a September 2012 study found an association between smoking pot and developing a severe type of testicular cancer. It should be noted, though, that this was a link and does not necessarily indicate a causal relationship.

Oddly, one study actually linked marijuana use to a reduced risk of cancer. According to the study, published in Cancer Prevention Research, 10 to 20 years of marijuana use was associated with a significantly reduced risk of head-and-neck squamous-cell carcinoma.

Recent research does suggest cigarette smokers are taking more of a risk by smoking marijuana; studies found the greatest precancerous abnormalities in those who smoke a combination of the two.


Respiratory problems

A significant amount of research has linked long-term cannabis use to respiratory issues. According to the American Lung Association, those who frequently smoke pot but do not smoke cigarettes have more health problems and miss more days of work than nonsmokers, with many of those sick days due to respiratory illnesses. This is because long-term marijuana use increases the risk of chest illness and lung infections, and can lead to bronchitis.

Like tobacco smokers, marijuana smokers can develop chronic coughing and more of that gross phlegm in the back of the throat.

On the positive end of the research spectrum is a January 2012 study, published in the Journal of the American Medical Association, that studied 5,115 adults over a period of 20 years and found that men who smoked one joint every day for seven years had a 1.6% higher lung capacity than that of men who didn’t smoke pot.


Fertility problems

A solid amount of research has found that heavy use of marijuana reduces men’s testosterone levels, as well as sperm count and quality. There’s also a possibility that heavy-smoking men could experience a lowered sex drive and decreased fertility.

Women aren’t necessarily in the clear when it comes to marijuana’s effects on the reproductive system either. According to Brown University, research has linked heavy marijuana use to irregular periods, which could result in a decreased ability to conceive but not cause complete infertility.


Heart problems

Because of the short-term effects on heart rate, smoking marijuana increases one’s risk of heart attack in that first hour after taking a hit.



You’ve probably heard this old one before: Smoking pot could make you schizophrenic. Well, not exactly. For those who already have schizophrenia, marijuana could trigger schizophrenic episodes, but there’s no substantial evidence to prove it can cause the actual disorder.


Reduced risk of obesity

You would think there would be an increased risk of obesity in pot smokers considering how marijuana tends to make people unusually hungry. Not so, according to a 2011 study that found a lower rate of obesity among those who smoke pot.


Impaired cognitive functions

We know what you’re thinking: “Of course pot impairs cognitive functions! That’s kind of the point!” But in the long term, regular marijuana use has been found to weaken smokers’ ability to learn and remember information by impairing their ability to focus, sustain and shift attention. Additionally, one study linked long-term use with a reduced ability to organize and integrate complex information.

As you probably already know, it’s definitely not a good idea to drive high — or under the influence of any drug that affects the cognitive abilities required to operate a vehicle. Research has shown that marijuana impairs braking time, attention to traffic signals and other driving behavior, which can last for 12 to 24 hours because of THC accumulation in fatty tissue.



Anyone who tells you pot isn’t addictive is wrong. Like many drugs, it can be. One in 300 American adults are addicted to marijuana, and about 9% of users become addicts. For reference, this compares to 10% of drinkers who are likely to become alcoholics.

An increasing number of studies have discovered marijuana can cause physical and psychological withdrawal symptoms, including irritability, restlessness, insomnia, nausea and intense dreams. And tolerance increases quickly with the drug, meaning people need increasingly more of it to get the same effect — specifically, heavy users need eight times more to get the same effects as infrequent users, according to Brown University.



One of the positive attributes of marijuana use is that it’s practically impossible to overdose on it. You would need to smoke an absolutely insane amount of the drug to OD — the Good Drugs Guide states it would take thousands of times the amount needed to get high for the dose to be fatal.