What marijuana researchers have to say about 420

(CNN) — It’s 420 or “weed day,” and people around the world will be paying homage to their favorite guilty pleasure: marijuana.

Currently, 24 states, two territories and the District of Columbia in the United States have legalized marijuana for recreational use, making it that much easier for people to take a toke or pop an edible at 4:20 p.m. on April 20 (if not all day).

But not everyone joins in on the 420 festivities. Some scientists who study weed have become increasingly concerned about the potential harm cannabis can do to the body, especially when smoked or vaped.

“When you burn something, whether it is tobacco or cannabis, it creates toxic compounds, carcinogens, and particulate matter that are harmful to health,” Dr. Beth Cohen, professor of medicine at the University of California, San Francisco, told CNN previously via email.

Marijuana smoke may even be more harmful than tobacco because users hold the hot smoke in their lungs longer to maximize their high, Cohen said. A March 2021 study found teens were twice as likely to report “wheezing or whistling” in the chest after vaping marijuana than after smoking cigarettes or using e-cigarettes.

“I’m in Colorado, and on 420 the smoke billows out of places where people gather to celebrate — it’s like a factory smokestack,” said Robert Page II, a professor of clinical pharmacy and physical medicine at the University of Colorado Skaggs School of Pharmacy and Pharmaceutical Sciences in Aurora.

“I worry when people are in an enclosed space because new data is beginning to show that secondhand marijuana smoke may be just as dangerous as the primary smoke,” Page said. “Like tobacco, cannabis affects the central nervous system, and there are side effects which tend to primarily be cardiovascular in nature.”

Any level of marijuana use raises the risk of stroke by 42% and heart attack by 25%, even if there is no prior history of heart disease and the person has never smoked or vaped tobacco, a recent study found. Weed has also been linked to cardiac arrhythmias such as atrial fibrillation; myocarditis, which is an inflammation of the heart muscle; spasms of the heart’s arteries and a higher risk of heart failure.

A lack of knowledge about weed

Despite these health concerns, the majority of American adults still believe smoking or vaping marijuana smoke or breathing secondhand smoke from a joint is safer than tobacco smoke, even if children are present, according to an August 2023 study.

It’s not.

“If a person is in a closed space with marijuana smokers, they can test positive for cannabis in their urine. They can also get some of the other physical effects of marijuana, including an increased heart rate and feeling ‘high,’ ” Carol Boyd, founding director of the Center for the Study of Drugs, Alcohol, Smoking and Health at the University of Michigan in Ann Arbor, told CNN in an earlier interview.

It’s not just your lungs that may be at risk. A January 2021 study found people who only smoked marijuana had higher blood and urine levels of several smoke-related toxins than nonsmokers. Those toxins are linked to anemia, liver and neurological damage, cancer and other health issues.

There’s more: Weed users are nearly 25% more likely to need emergency care and hospitalization, according to a 2022 study, and overuse of marijuana can lead to complications when in surgery. Weed users have more heavy metal in their bodies. Serious traffic accidents are on the rise in areas where weed is legal, a 2023 study found.

Potency of weed has skyrocketed, which can heighten health risks and is leading to a global rise in marijuana addiction as well as marijuana use disorder.

“Approximately 3 in 10 people who use marijuana have marijuana use disorder,” according to the US Centers for Disease Control and Prevention. Experts say this condition comes with a higher risk of mental disorders, cognitive deficits, use of psychiatric services and violent behavior.

Weed’s impact on babies and teens

Using marijuana during pregnancy has been linked to low birth weight, one of the strongest predictors of a child’s long-term health.

Babies born to mothers who smoke pot or eat edibles to control nausea, for example, were twice as likely to be premature and 2.5 times as likely to be admitted to a neonatal intensive care unit, according to a 2023 study. Just as alarming: A 2020 study found children born to marijuana users had more psychotic-like behaviors and more attention, social and sleep problems as well as weaker cognitive abilities.

It’s not good for older children, either. The growing use of weed by adolescents is extremely alarming, experts say, because marijuana is known to damage the developing brain.

“The teen brain is actively developing and continues to develop until around age 25,” the CDC states on its website. Use during that time can have permanent effects such as damage to learning, memory, problem-solving skills and the ability to pay attention, the CDC said.

“It’s disruptive to the teenage brain, so it needs to be used with extreme caution or not at all,” said Dr. Peter Grinspoon, a primary care physician and cannabis specialist at Massachusetts General Hospital in Boston who authored “Through the Smoke: A Cannabis Specialist Untangles the Truth About Marijuana.”

Young people who use marijuana are more likely to develop long-lasting mental disorders, including depression, social anxiety and schizophrenia, and drop out of school, the CDC said. Studies show overuse of marijuana by youth with mood disorders leads to a rise in self-harm, suicide attempts and death.

Daily use by adolescents and adults can result in another unpleasant side effect: uncontrollable vomiting, according to a 2021 study.

“They vomit and then just continue to vomit whatever they have in their stomach, which can go on for hours,” study author Dr. Sam Wang, a pediatric emergency medicine specialist and toxicologist at Children’s Hospital Colorado, told CNN previously.

Despite these concerns, school-age kids were vaping twice as much weed in 2020 as they did in 2013. In fact, some parents told doctors they believed vaping marijuana was safer than tobacco, Boyd told CNN earlier via email.

“You seem to believe that heating chemicals (including carcinogens) into a vapor and inhaling them is healthy? My answer is, ‘No, it is not a healthy behavior.’”

In addition to harming the lung, vaping weed is associated with a dangerous, recently identified lung disease called EVALI, short for e-cigarette, or vaping product use-associated lung injury. By early 2020, the CDC had recorded over 2,800 hospitalizations and 68 deaths due to this condition, according to Yale Medicine.

Is there nothing good about pot?

Studies do show there are some medicinal benefits from weed. An August 2023 review of literature found cannabidiol, or CBD, reduced seizures in epilepsy. In addition, some cannabinoid mixtures may benefit multiple sclerosis, nausea from chemotherapy, chronic pain and inflammatory bowel disease, “but not without adverse events,” according to the study.

Those “adverse” effects may actually be less than the impact of traditional medications, said Grinspoon, who is on the board of the advocacy group Doctors for Drug Policy Reform, which addresses cannabis, psychedelic and drug regulation in general.

“People are eating cannabis instead of more dangerous medications like opioids and benzodiazepines (medicines used for anxiety and seizures), which are either addictive or have terrible side effects,” he said. “People are also able to cut down on their nonsteroidals, which are not without harm.”

However, there’s a note of caution in that upbeat take. Studies may use purified synthetic cannabis that is not at all like weed purchased off the street, said the University of Colorado’s Page.

“Even what is bought in stores may not be what it appears,” Page said. “While the regulatory agencies do look for things like adulteration, for the most part it’s not really regulated in terms of knowing what the exact amount of CBD or THC is in an over-the-counter product.”

There’s another point: Many people use medicinal edibles when they want pain relief that lasts over time and may turn to a puff when in need a quick hit of relief, Grinspoon said. Eating marijuana or using a tincture bypasses the harms to the lungs; unfortunately, there has been little research on the benefits or harms of using edibles or other options.

Little neutral research on pot

There’s a reason for the lack of research. Studies since the 1950s have typically been green-lit for funding only if they were exploring the negative side of marijuana use, experts told CNN.

On a federal level, cannabis is still classified as a schedule I substance, the highest level of drug restriction. Researchers must still navigate yards of red tape to get approval from a variety of federal, state and local agencies before a study can start.

“Particularly during and after the Nixon administration, researchers could only get money if they focused on the negative consequences,” Boyd said. “Each new generation of researcher followed in their mentor’s footsteps and focused on the negative health consequences.”

Another hurdle was getting legal access to marijuana to study it. For more than 50 years, the federal government only permitted the University of Mississippi to grow cannabis for research. Supply couldn’t keep up with demand. It took the US Drug Enforcement Administration until 2021 to begin the search for additional facilities to grow the plant for scientific use.

Statewide legalization of recreational marijuana in the last decade has opened a new avenue of scientific inquiry — observational studies in which researchers can ask people about their marijuana use and expect a mostly truthful response. Scientists can now cross-reference insurance, medical and safety data with reported marijuana use to see how it affects the body over time.

“There were 4,000 studies about cannabis done over the last two years; that’s a ton of research,” Grinspoon said. “I think it’s more neutral, and it’s coming from independent think tanks and academia and not just from the cannabis industry.

“I think it’s much better now that it’s out of the shadows, and people can be honest when they go to the doctor when they need help,” he added. “In the past, if you’re in the ER and vomiting, you couldn’t say, ‘I was using marijuana.’”

Still, at this point, Page said, the data is what it is.

“There’s no data to support any benefits of recreational use of marijuana, while there is data to support the use of cannabis for some medicinal purposes.”