Health

Is Marijuana As Safe As We Think? Experts Reveal What's Still Largely Unknown

Despite its emerging popularity and purported health benefits, there’s a lot about cannabis safety in humans we don’t know.

A pair of gloved hands holding a scoop of freshly ground cannabis against a dark background in a lic...
Mike Sweeney Photography/Moment/Getty Images

In the not-so-distant past, marijuana was cast as the nefarious antagonist in the saga of American drug policy, demonized by anti-drug campaigns and sensationalized commercials of teenage drug dealers luring their peers to ruin. Since the legalization of cannabis for medical use in California in 1996 and, later, recreational use by various states in 2012, the devil’s lettuce lost its sinister reputation, instead gaining increasing public support. In fact, seven in 10 Americans believe marijuana use should be legalized, according to a 2023 Gallup poll; cannabis use among adults aged 35 to 50 reached a historic high in 2022 at 28 percent, from 13 percent a decade prior.

Support is fed into marijuana’s laundry list of supposed health benefits: reducing anxiety, alleviating chronic pain, and treating debilitating mental health conditions like post-traumatic stress disorder. This seeming panacea-esque portrayal has quickly catapulted “Mary Jane” to mainstream use and high consumer demand.

Despite this, we have very little evidence supporting marijuana’s safety in humans. In fact, there’s emerging research suggesting cannabis use, whether medically or recreationally, poses a strong risk for undesirable cardiovascular outcomes like heart attack and stroke or detrimentally affects brain development in adolescents and, to some extent, adults. Marijuana has also been linked to negative impacts on male fertility and possibly weakening the immune system.

Does this mean all forms of marijuana use are bad? Not necessarily, says R. Lorraine Collins, a psychologist at the University at Buffalo and director of its Center for Cannabis and Cannabinoid Research. “It’s a very complicated question,” Collins tells Inverse. “It’s one of the things I want to get people to understand that this is not a yes or no question. Cannabis is very much a mixed bag.”

Is marijuana good for you?

Marijuana contains over 100 chemicals called cannabinoids, the two well-known being cannabidiol (or CBD) and tetrahydrocannabinol (or THC). These two chemicals interact with your body in different ways, with THC responsible for most of marijuana’s psychological effects and CBD being non-psychoactive. Researchers used to think CBD counteracts or balances out THC’s negative effects, like anxiety and paranoia. However, new research in recent years suggests that doesn’t seem to be the case, and at least when consuming cannabis, high doses of CBD prevent the breakdown in THC, making the drug’s sensations last longer.

RUNGROJ YONGRIT/EPA-EFE/Shutterstock

It’s believed these cannabinoids interact with the body’s endocannabinoid system (or ECS), an ancient cell signaling network crucial for maintaining homeostasis in the brain and throughout the body. Receptors for this system were first discovered in the late 1980s, alongside the discovery that we naturally produce cannabinoids, called endogenous cannabinoids (endocannabinoids for short).

Some studies have found that cannabinoids like THC and CBD may have therapeutic benefits. For example, cannabis may help treat or prevent nausea and vomiting associated with cancer drugs. One such synthetic THC, called dronabinol, was approved by the U.S. Food and Drug Administration in 1985. Early evidence from laboratory and clinical studies and anecdotal reports found marijuana may help with controlling seizures. In 2018, this led to the FDA approving Epidiolex, an oral solution containing CBD (obtained through hemp, a variety of cannabis), for severe epilepsy.

For conditions like chronic pain, whether marijuana is helpful becomes a bit murkier and elusive. Two systematic reviews published in 2017 by the journal Annals of Internal Medicine found there wasn’t enough scientific evidence cannabis could alleviate pain connected to nerve damage, called neuropathic pain, and that there was even less research supporting the benefit of marijuana for treating PTSD, Inverse previously reported.

This lack of conclusive evidence is emblematic of the current state of marijuana research, says Robert Page, a professor in the departments of clinical pharmacy and physical medicine at the University of Colorado Anschutz Medical Campus.

“The problem is that a lot of the data that are published are retrospective [looking back at existing data] or observational,” Page tells Inverse. “What that means to the lay public is that I can only say with confidence that 95 percent of the time, this is an association, not necessarily a causation.”

An employee holds bottles of Epidiolex, a cannabinoid-based medicine, at the GW Pharmaceuticals Plc facility in Sittingbourne, U.K. The country is the biggest producer of cannabis for medical and scientific purposes, according to the United Nations.

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In 2017, Collins and colleagues at various academic institutions co-wrote a report published in the National Academies of Sciences, Engineering, and Medicine that reviewed thousands of cannabis studies and found that there was a huge gap in the knowledge about the risks and benefits of cannabis use.

Collins says what underlies this huge gap is the lack of human studies, which are currently difficult to conduct since marijuana is still classified as a Schedule I controlled substance, which also includes heroin, lysergic acid diethylamide (or LSD), and ecstasy.

“[The federal regulations] have been a huge barrier to getting human research and, as an alternative, you see animal research, especially in areas like, for example, the effects of cannabis on the fetus,” she says.

What cannabis studies currently show about safety

For some individuals, depending on their exact medical needs, cannabis could be a source of great relief, according to all experts Inverse spoke to for this story. But right now, to rubberstamp its consumption as safe — especially if it’s vaped or smoked — would be ignoring all the warning signs that have emerged thus far, as well as the unknowns of short- and long-term marijuana use.

“It seems to me that we’re putting the cart before the horse, that we’re recommending it, and states are selling without the necessary evidence to support [its use],” Deepak D’Souza, a psychiatrist and director for the Science of Cannabis and Cannabinoids at the Yale School of Medicine, tells Inverse.

For the heart, multiple studies link cannabis with a myriad of debilitating and potentially life-threatening conditions. A 2024 study published in the Journal of the American Heart Association found that smoking, vaping, or even ingesting marijuana was associated with a significantly higher risk of heart attack and stroke, even if you don’t have a history of pre-existing heart conditions. The study found that daily and non-daily cannabis users had an increased risk of heart and stroke compared to nonusers, but the stroke and heart attack risk went up 42 percent and 25 percent, respectively, for daily users.

“The problem is that at this point, from a cardiovascular standpoint, there are no cardiovascular benefits with cannabis. We have no data to back that up, period.” says Page, adding that instead, these cardiovascular outcomes are often undesirable side effects of when cannabis is used to treat other symptoms like nausea or pain.

Smoking marijuana, regardless of the manner smoked, can scar and damage the lungs, according to the Centers for Disease Control and Prevention.

picture alliance/picture alliance/Getty Images

As cannabis use among adolescents and teens has increased since 2000 — by as much as 245 percent, according to a 2022 study — the drug’s effect on the developing, as well as adult, brain has researchers deeply concerned, says Collins and D’Souza. Studies have found regular marijuana use in adolescents associated with altered brain connectivity and reduced brain volume in regions involved in cognitive and executive functions like memory and impulse control. (This makes sense as the adolescent brain is still developing.) For adults, while some studies have been conflicting, finding no significant structural brain differences between users and non-cannabis users, other studies following long-term marijuana use found that the drug can cause functional cognitive impairments. This depended, however, on the age that someone started using, how much they used, and how often.

Pot may even influence our genetics and immune system. A 2023 study published in the journal Molecular Psychiatry found that recent and long-term marijuana use was linked to changes in the chemical restraints governing which genes are turned off or on, what’s called epigenetics. The study found that these epigenetic changes overlapped with those incurred from tobacco use, clued into biochemical pathways involved in cell growth, hormone signaling, resisting infection, and mental health disorders like schizophrenia and substance abuse disorder. One caveat, though, is that this study didn’t establish these epigenetic changes with any actual health outcomes.

For those looking to conceive, taking a daily edible may impact your fertility. In a 2022 study published in the journal Fertility and Sterility, researchers at Oregon Health and Science University found that healthy nonhuman primates who were given a THC edible daily over the course of 11 months (the dosage similar to what humans take), led to reduced testosterone levels and severe testicular shrinkage by almost 50 percent. It was unclear if those changes were permanent but a follow-up study in 2023 confirmed that discontinuing THC partly reversed these effects in the animals. There's some evidence also to suggest THC exposure may alter the menstrual cycle in monkeys, upsetting their ability to ovulate normally.

Then there’s the increased risk of psychosis and addiction linked to high-potency cannabis, as reported by a 2022 study in the journal The Lancet Psychiatry. This is especially concerning as the average amount of THC contained in retail cannabis today is much higher than during the 1970s: from around less than two percent to around 15 percent or more through sophisticated breeding techniques. However, in some concentrated products like oils, edibles, and shatter (a cannabis extract that resembles glass), THC content can be as high as 90 percent today, says D’Souza.

Cannabis dispensaries in states like New York City are contributing to the boom in retail marijuana.

Glasshouse Images/Shutterstock

Despite all these unknowns, marijuana use is unlikely to cease anytime soon. One 2024 report valued the cannabis market at nearly 30 billion U.S. dollars in 2022 and is expected to reach nearly 83 billion by 2027. What’s needed to keep pace with this explosive market and figure out a system of guardrails, say the experts, is loosening federal regulations that stymie scientific research. There may be some movement in that direction: In 2022, President Joe Biden called for a review of marijuana policy. This was followed a year later by the U.S. Department of Health and Human Services (HHS) asking the U.S. Drug Enforcement Administration (DEA) to consider reclassifying cannabis as a far less restrictive Schedule III drug. The DEA is expected to come to a formal decision sometime soon, NBC News reported in February.

For Page, recognizing that people use marijuana for a variety of reasons, whether medicinally or recreationally, and not passing judgment about their use is key to bridging awareness.

“From our standpoint [as health care providers], we need to inform the public about potential risks and dangers,” says Page, “and that’s what I try to do.”

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