is weed bad for you

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Let’s actually talk about the health effects of weed

Conventional wisdom is that smoking weed is essentially harmless, but what does the research actually say?


Cynthia McKelvey


Posted on Sep 5, 2017   Updated on Jan 26, 2021, 10:11 pm CST

Is weed bad for you? And as more states legalize it, are we going to see more weed-related diseases?

It’s conventional wisdom among stoners that smoking weed is, essentially, harmless to the lungs. Look up “lung cancer” on Reddit’s marijuana-enthusiast forum, r/trees, and you’ll find links to study upon study that finds no link between getting high and getting sick. At the same time, hacking your brains out after taking a huge bong rip can’t be good for you, can it?

The science behind using marijuana and our physical health is still developing. While studies that survey people for their weed habits and then try to correlate their answers with their health say that weed is harmless, other studies suggest otherwise. For example, one study found that marijuana smoke has just as many cancer-causing chemicals in it as tobacco smoke. Another found that marijuana smokers, like tobacco smokers, have evidence of inflammation in their lungs—a condition which can be a precursor to chronic obstructive pulmonary disease (COPD.)

And yet, there’s no evidence that people who smoke weed go on to develop lung cancer at the same rates as tobacco smokers, and evidence is conflicted about COPD. But as with all things in science, there’s more going on here than meets the eye.

Marijuana research is ridiculously complicated

Because the Drug Enforcement Agency still has marijuana listed as a schedule 1 drug, with “no currently accepted medical use and a high potential for abuse,” researchers have to go through the Food and Drug Administration, DEA, and the National Institute for Drug Abuse to obtain a license to study it.

Then there’s getting the pot itself. Until last year, researchers who wanted to study marijuana had to get it from the one and only DEA-licensed source: a farm at the University of Mississippi. The DEA lifted this restriction in 2016, but anyone who wants to grow marijuana for research still has to get licensed by the DEA first. A year later, the DEA has still not approved any new applications.

So what are researchers to do? It’s a lot of hurry-up-and-wait, according to Ellen Burnham, an associate professor of pulmonary and critical care medicine at the University of Colorado School of Medicine. In a phone interview with the Daily Dot, she recounted the agonizing process some researchers at the University have endured just to get a room set up to use for their marijuana research.


Hopefully, as the tides turn in favor of legalization, the DEA will continue to relax its restrictions on research, allowing scientists to tease apart the potential harms—and many potential benefits—of cannabis. But in the meantime, researchers get a lot of their data from just asking marijuana users about their habits.

“The data that’s collected in those larger epidemiological studies isn’t super detailed. And the questions don’t really get at how much are you using, how many grams, how many times per day,” Burnham said. “During the time that those studies were conducted, marijuana was more illegal than it is now, so the honesty of the reporting may have been affected as well.”

But let’s take a look at the data anyway.

Is weed bad for your lungs?

According to a 2013 review in the Annals of the American Thoracic Society, you’ve got (almost, probably) nothing to worry about when it comes to how weed’s going to affect your lungs. At worst, most marijuana smokers can expect chronic inflammation of the upper airways, called bronchitis.

“Chronic bronchitis does not necessarily lead to COPD,” the review’s author, Donald Tashkin, professor emeritus at the David Geffen School of Medicine, told the Daily Dot. “It has to do with the differential effect on large vs small airways. A major site of pathology in COPD resides in the small airways, which do not appear to be affected—at least functionally—by habitual marijuana smoking.”

Inflammation in those small airways is the key to developing COPD, and Tashkin noted that THC has well-documented anti-inflammatory effects. He believes that this property essentially protects the user from the inflammatory properties of marijuana smoke.

He has a similar theory for why marijuana users don’t develop lung cancer: THC and cannabidiol both have anti-tumor properties. So Tashkin believes that they essentially “cancel out” the effects of the carcinogens in the rest of the marijuana smoke.

“I don’t know how you would completely ‘cancel out’ all the other potentially harmful things contained in combustion products with ONLY [sic] THC. This seems overly simplistic,” Burnham said in an email to the Daily Dot. “Stuff in smoked cigarettes and cannabis is carcinogenic. In a nutshell, at this point in time, I’m not aware of any pathways or molecular targets whereby THC can reliably ‘block’ development/worsening of either COPD or cancer in humans.”

Burnham believes it’s only a matter of time before we start seeing more harmful effects of marijuana. It could be that time is the issue here, in fact. COPD and lung cancer both take quite a bit of time to develop. But most human studies have only looked at people in their 20s and 30s—long before lung cancer and COPD would crop up.

Tashkin said that he wouldn’t be altogether surprised if, in a bit longer, he started to see more harmful effects of marijuana on the lungs. He also noted that older people, who may be encouraged to smoke weed after it becomes legal in some states, may also be more vulnerable to COPD.

He also noted that the immune-suppressing effect that may protect people from COPD may, in turn, open up the airways to the opportunity for infection and that some people may develop pneumonia.

Are dabbing or vaping safer?

While there’s relatively little data on how smoking affects the lungs, there is even less on vaping and dabbing. While vaping tobacco may potentially be healthier for the lungs, it’s not clear of vaporizing weed has the same degree of benefit.

Essentially, Tashkin argues in another paper, the amount of damage you’re saving yourself by vaping is minimal since, in his view, smoking marijuana is not that bad for you to begin with.

“It’s logical that vaping could be [safer,] but I’ve read horrible case reports,” Burnham said. She cited one where a man required ventilator support after vaping marijuana, despite being an experienced user. “I don’t think there’s any absolutes here.”

Same goes for dabbing. It’s not clear if, when used, dabs—highly concentrated THC oil—are any better that marijuana vaporized or smoked. But at least one user found himself in the hospital needing treatment for lung injury after dabbing.


Other researchers are concerned with the potential mental effects using such high concentrations of THC might have on the brain. While marijuana is associated with psychosis, it’s unclear if the relationship is cause-and-effect, or if marijuana use may just coincide with when many mental disorders crop up anyway.

Tashkin also noted that marijuana users tend to “self-titrate.” In other words, they tend to moderate their own doses of THC depending on their tolerance and how high they want to get at any given time. So, in his view, people who dab probably ultimately consume as much or even less THC than people who smoke joints—it’s all just a matter of their preferred method of smoking.

Of course, the drugs in cannabis don’t only affect your lungs.

Weed increases the risk of heart attack of stroke

Recently, researchers showed that using marijuana was associated with an increased risk for “hypertension mortality,” which, in normal human words, means that people who smoked weed were a bit more likely to die due to having high blood pressure than people who didn’t. The study was also criticized for defining “regular marijuana use” as having ever smoked in your life, but that doesn’t mean we should throw the findings out just yet.

There are other case reports that have shown an association between using cannabis and strokes. In many of these reports, the amount of weed used may be underestimated, and there are also factors to consider, like alcohol and tobacco use.

Smoking weed also increases the heart rate and may also increase the risk for heart failure four-fold within an hour of smoking. Of course, that’s a four-fold increase on an already very small risk if you’re an otherwise healthy young adult.

So, is weed bad for you?

The myriad health effects and benefits of marijuana are likely due to the fact that the plant has about 90 to 100 different active drugs in it. Some of those might be really helpful and treat things like anxiety, epilepsy, or nausea.

And others may cause much worse problems, like nausea and vomiting that don’t go away even after abstaining from pot. Burnham noted that there seems to be an upswing of such cases in hospitals. She told the Daily Dot about one patient who had been admitted to the hospital several times in a year due to intractable nausea and vomiting, each time becoming so dehydrated that his kidneys began to malfunction. And researchers are at a loss for why it happens to some patients.


According to one review, there are also some cases of short- and long-term psychosis that seems to be triggered by pot. For people who have an established psychotic disorder, like schizophrenia, marijuana can trigger relapse and make their symptoms worse.

But there’s still just so much we don’t know.

“I wish that the federal government and state governments as well would reconsider their leniency in terms of having qualified investigators conduct some of these studies without all the red tape,” Burnham said. “It’s just so hard to do research with human subjects, but this takes it to a whole new level.”

The lack of data means doctors don’t really know how to best advise their patients. If a young patient comes in and asks his doctor what is likely to happen if he uses marijuana, what will the doctor really be able to say? It could be fine, or it could trigger underlying schizophrenia. You could be fine, or you could have a heart attack.

No drug, legal or not, is completely without risk. But without the ability for scientists to conduct proper, well-controlled studies, we’ll never fully understand the risks—and benefits—of smoking weed.

Nonetheless, marijuana laws are relaxing across the country. More states legalize marijuana for medical and recreational purposes every election.

“The states themselves are making money, but they’re not really underwriting the research to say, ‘What are we really doing to the health of our population?’” Burnham said.

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*First Published: Sep 5, 2017, 6:30 am CDT