With more states moving toward decriminalizing marijuana, the era of pot prohibition is waning in the United States. Yet even as use of the drug becomes more accepted, both for medical and recreational use, questions about marijuana side effects remain.
“The U.S. government has held back the medical community’s ability to conduct the type of research that the scientific community considers the experimental gold standard in guiding medical practice. Thus, the use of cannabis for medical treatment is happening in states based largely on anecdotal or limited science,” a 2015 report from the Brookings Institution noted. Currently, the federal government’s stance on marijuana makes it difficult for researchers in the United States to study marijuana use and its side effects.
Legal hurdles haven’t totally stopped research into marijuana side effects, especially outside the U.S., and these scientific efforts provide some insight into what happens to your body when you consume this popular drug. Anecdotal reports from marijuana users also provide some idea of the consequences of using pot, though it’s often impossible to know whether a side effect someone attributes to weed is really caused by the drug or due to an unrelated factor.
To give you an idea of some of the worst marijuana side effects people experienced, we turned to Reddit, where people have shared their stories about the less pleasant aspects of pot. Of course, these side effects aren’t guaranteed to happen to everyone who uses marijuana. Some are related to the specific way the drug was consumed, while others were mostly experienced by very heavy users. Still, for those who are curious about the downsides of smoking a joint, here are five marijuana side effects users complained of, as well as what science says about each issue.
1. Loss of appetite
Everyone knows marijuana can trigger a case of the munchies, but some users complain they find their appetite disappears when they aren’t using the drug.
“I find that I don’t have much of an appetite any more unless I am stoned,” wrote Reddit user oz24. “[T]hinking about eating sober gave me nausea. [Probably] the worst part of all the side effects,” echoed user newmilwaukee.
Scientists who study the relationship between marijuana and appetite have discovered that a component of the drug appears to activate hormones that produce hunger, but it’s not clear what effect that might have on a person’s desire to eat when they weren’t high. A separate study found that people who smoked weed at least three times per week were skinnier than people who didn’t use marijuana, but why that is the case isn’t clear.
2. Lung collapse
“I suffered from a collapsed lung in 2013. It’s not clear how much marijuana was the cause but I’m pretty positive it helped aid the process of it happening,” wrote astralcars04.
Anecdotal evidence aside, collapsed lung (a condition known as pneumothorax) has “not been definitively linked to marijuana smoke,” according to the Alcohol and Drug Abuse Institute at the University of Washington, though some small studies point to an association between lung collapse and marijuana use. A report in the Journal of the Royal Society of Medicine also described a case of a collapsed lung in a heavy pot smoker, but doctors couldn’t be sure the lung collapse was due to the person’s marijuana habit.
3. Breathing problems
Some frequent weed smokers complained of trouble breathing and other lung problems on Reddit. “I smoked weed pretty heavily for around 13 years and I mostly smoked out of bongs. After a few years of smoking I started noticing that I was coughing up nasty black tar in my phlegm,” wrote legalize 420. “My lungs aren’t as functional as they used to be,” wrote thaCaseyB.
Despite complaints from users, it’s not clear that smoking marijuana causes serious respiratory problems. A 2015 study published in the Annals of the American Thoracic Society found that smoking one joint per day for 20 years didn’t have a significant negative effect on lung health. However, smoking pot was associated with symptoms such as coughing, sore throat, and shortness of breath.
4. Trouble focusing and fuzzy memory
“I was a very outgoing guy before I started, then I kind of imploded after smoking a lot over 4-5 years. Ever since I’ve stopped, I feel clearer but I still can’t maintain a conversation like I use to and my thoughts are cluttered. To be honest, it almost feels like my thought structure is corrupt or fragmented, and I can’t put together sentences like I use to,” wrote brettzky10. “Biggest side effect I’ve noticed is my short term memory. It’s horrendous. I struggle to find the right words, and I also get a wee bit confused if the subject is deep in any way,” said cavalier_hat.
Heavy pot use can cause permanent damage to your short-term memory, researchers at the University of Lausanne, Switzerland found. The researchers looked at the marijuana use habits of 3,400 Americans over a period of 25 years. They found that those who smoked daily for five years or more had worse verbal memory in middle age than people who used the drug less frequently or not at all. Other cognitive functions, like focus, weren’t affected. The researchers also noted that there was no way to prove the link between pot and short-term memory; it is possible people with poorer cognitive function were more likely to become heavy marijuana users, for example.
5. Anxiety and paranoia
Tales of pot-induced paranoia aren’t unusual. “I smoked weed for about 6-7 years and eventually had to quit entirely because I became SUPER anxious, paranoid and self-conscious,” one Reddit user recounted. “[A]fter about 3/4 years of semi heavy use the high just changed now it just sends me loopy with bouts of anxiety and paranoia and just completely over thinking every aspect of my life until I can put a negative spin on it,” wrote blue_skies.
Science says the relationship between marijuana use and paranoia isn’t a myth. A 121-person study conducted at the University of Oxford found that people were more likely to experience paranoid thoughts after ingesting THC, the active ingredient in cannabis, than those who took a placebo. The drug also triggered anxiety, negative thoughts about the self, and lowered mood.
“There’s certainly evidence that if you use cannabis — particularly when you’re young — and you use it a lot, that this can put you at risk for later problems,” professor Daniel Freeman, who led the study, told WebMD. But paranoia isn’t an inevitable side effect of smoking weed, he added. “[I]f you have greater confidence in yourself, you improve your self-esteem, and if you try not to worry or ruminate about potential threats in the world … then the effects of the THC should hopefully be less capable of inducing paranoia.”