Risk and Relief: Reckoning With The Complicated Side Effects Of Cannabis

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One of Ellen Smith’s favorite activities is to walk with her service dog Velma along the bay near her home in North Scituate, RI. The active retiree also swims and gardens despite living with a form of Ehler-Danlos syndrome, a genetic disorder that weakens connective tissue and causes loose, unstable joints. Smith credits her mobility to a nightly dose of oil made from marijuana plants, which she says reduces her pain and helps her sleep.

“I’m doing better at 74 than I was 10 years ago,” says Smith. “And I’m grateful for it.”

Relief of insomnia, as well as mild-to-moderate pain, are some of the most effective uses of medical marijuana, or as it is more commonly referred to these days, medical cannabis, says Jordan Tishler, M.D., an instructor at Harvard Medical School and internal medicine doctor specializing in cannabis medicine.

“Medicines by their nature are a double-edged sword,” says Dr. Tishler. “If they’re going to change your body chemistry, then it can be a change for good or for bad.”

The risks of using cannabis for medical issues or recreationally range from short-term effects, such as intoxication and impaired thinking, to longer-term effects, including gastrointestinal issues, lung issues, and an increased risk of heart attack and stroke. And while many believe cannabis is nonaddictive, cannabis use disorder is a real and prevailing issue, particularly among those who start smoking in their teen and young adult years.

The History and Legal Landscape of Cannabis

Cannabis sativa is one of the world’s oldest cultivated plants and has likely been used medicinally for centuries. The cannabis plant contains more than 100 compounds called cannabinoids. The best studied of these are Delta-9-tetrahydrocannabinol (THC), which has mind-altering effects that can affect mood, thoughts, and perceptions of reality, and cannabadiol (CBD), which does not cause intoxication.

In addition to relieving chronic pain and insomnia, evidence suggests that cannabis may also help with other conditions, including anxiety, post-traumatic stress disorder, Tourette syndrome, nausea and vomiting caused by cancer treatment, lack of appetite and weight loss due to HIV/AIDS, and stiff muscles and spasms associated with multiple sclerosis, according to a comprehensive report published by the National Academies of Sciences, Engineering, and Medicine in 2017.

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In 2018, the U.S. Food and Drug Administration (FDA) approved one drug derived from the cannabis plant, Epidiolex (cannabidiol), to treat seizures from certain rare forms of epilepsy. The agency has also approved three synthetic (man-made) drugs to increase appetite and reduce nausea associated with certain health conditions and treatments: Marinol (approved in 1985) and Syndros (approved in 2016), both of whose active ingredient is dronabinol, a synthetic form of Delta-9 THC; and Cesamet (approved in 1985), with the active ingredient nabilone, another synthetically derived compound that is chemically similar to THC. Aside from those four FDA-approved medications, which providers can legally prescribe throughout the U.S., the legalities governing medical cannabis remain tricky.

Can Doctors Prescribe Cannabis?

In the U.S., cannabis products containing more than 0.3% THC are illegal at the federal level due to cannabis’s classification as a Schedule I drug under the Controlled Substances Act. However, the federal government has largely deferred to individual states to establish and enforce their own cannabis laws.

Except for FDA-approved medications, physicians cannot prescribe cannabis products, says Dr. Tishler—even in states that have legalized its medical usage. What physicians can do, he explains, is recommend specific types of products and doses, as well as certify that their patient has a medical condition that qualifies them to receive a medical marijuana card from their state.

The Stark Surge of Ultra-Potent Products

Generally speaking, cannabis carries greater risks at high doses, says Deepak D’Souza, M.D., a professor of psychiatry at the Yale School of Medicine and director of the Yale Center for the Science of Cannabis and Cannabinoids. And given the potency of products available today, it’s all too easy to take too much.

“What is perhaps most important for people to be aware of is that the cannabis that someone may have used 30 years ago is very different from the cannabis that’s currently available,” says Dr. D’Souza.

Both the strains of plants grown today, as well as the processing methods, have ramped up the potency of both medical and recreational products. Modern cultivation, such as hydroponics (a method of growing plants in nutrient-rich water instead of soil) and selectively controlled environments that maximize light and humidity, have allowed growers to increase the health and potency of their crops. Additionally, newer extraction methods, such as CO2 and ethanol extraction, are used to create highly concentrated cannabis-derived products like oils and waxes.

Studies of marijuana products seized by the Drug Enforcement Agency show that the potency increased from about 4% THC in 1995 to 17% in 2017. And it continues to rise, says Dr. D’Souza. The THC content of some dabs (cannabis concentrates that are heated and smoked), edibles, and oils is as high as 90 percent.

Such high potency is particularly problematic for older adults, who metabolize drugs more slowly than younger individuals and whose brains can be especially vulnerable to the effects. As an example of the potential impact of cannabis on older adults, Dr. D’Souza points to a 2023 study published in the Journal of the American Geriatrics Society showing that emergency department visits associated with cannabis among California adults aged 65 and older increased by nearly 2,000% from 2005 to 2019.

The Side Effects of Cannabis: From Mild Discomfort to Life-Altering Conditions

Most people are familiar with the “typical” side effects of cannabis: mild drowsiness, sleepiness, and the psychoactive “high” that recreational users often seek. However, the varying potencies, methods of consumption—whether smoking, vaping, or eating edibles—and the duration of use can all conspire to reveal a far broader spectrum of potential side effects. Many of these side effects, which include the very real issue of cannabis misuse (when a person can’t stop even when the drug is adversely affecting their health, work, or social life), remain under-researched—despite the growing prevalence of cannabis and its increasing acceptance within the medical community.

While the CBD component of cannabis doesn’t appear to cause serious side effects on its own, the drug can interact with a long list of supplements, herbals, and over-the-counter and prescription medications. CBD can intensify the drowsiness associated with anti-anxiety medications, sleep drugs, and herbals such as melatonin, for example. And it can interfere with the liver’s ability to process medications, so that you wind up getting too much or too little.

The THC component, on the other hand, is associated with numerous potential side effects. The most common short-term effect of cannabis products containing THC is intoxication, that euphoric “high,” says Dr. Tishler. While many people may enjoy the sensation, this intoxication can impair thinking, memory, and coordination, which can make you less safe behind the wheel of a car or operating heavy machinery. That effect can be minimized, he says, by starting at very low doses.

For those looking to use cannabis in a strictly medical capacity, Dr. D’Souza agrees that patients should avoid potent products. “For most people, THC produces a sense of relaxation or reduces anxiety,” Dr. D’Souza continues. “But for reasons we don’t fully understand, some people experience the opposite.”

Dr. D’Souza cautions that while inhaled cannabis takes effect quickly, edibles can take up to 90 minutes for their full impact to emerge. This delay often leads people to mistakenly believe their first dose isn’t working, prompting them to take too much. Additionally, higher doses increase the risk of severe intoxication, or what Dr. D’Souza calls a “bad trip” — a state marked by confusion, disorientation, dizziness, loss of coordination, panic, or paranoia.

Severe Mental Health Effects

In rare cases, some cannabis users can experience hallucinations or lose contact with reality. Research suggests that certain people may be more vulnerable than others to these severe mental side effects.

For example, a recent analysis in the journal Nature that pooled data from 162 studies found that teens and young adults with a history of mental health problems, as well as those exposed to high levels of THC, are more likely to experience psychotic symptoms. And males aged 16 to 25 who use cannabis may be particularly susceptible to developing schizophrenia, according to a study of the health records of nearly 7 million people living in Denmark.

Serious Heart Complications

Potential short-term cardiovascular effects of using cannabis include a faster heart rate, heart rhythm abnormalities, and, depending on the person, a rise or fall in blood pressure, says Dr. D’Souza.

Over the long term, says Dr. D’Souza, evidence suggests that cannabis could have more serious heart effects. A 2024 analysis of 430,000 U.S. adults published in the Journal of the American Heart Association found that, even after controlling for tobacco use and other heart risk factors, cannabis use was associated with a risk of heart attack and stroke. The risk was greater for those who used cannabis more frequently.

Lung Problems

Smoking cannabis has its own set of risks. Like the smoke from cigarettes and tobacco vapes, cannabis smoke irritates the lungs and contains cancer-causing substances and other toxins.

Long-term cannabis smoking is associated with chronic bronchitis and other lung problems, as well as an increased risk of developing cancer in the head, neck, and throat.

Cannabinoid Hyperemesis Syndrome (CHS)

While cannabis can affect your brain in ways that reduce nausea and vomiting, it can actually have the opposite effect on your gut. And over time, receptors in the brain may stop responding as well to the drug. That may be why long-term, heavy use of cannabis sometimes leads to a condition called Cannabinoid hyperemesis syndrome (CHS), which causes repeated, severe episodes of nausea, vomiting, and stomach pain.

If not treated, CHS can cause dehydration, kidney damage, and low blood levels of potassium, chloride, and sodium, minerals that maintain muscle and nerve function and control the amount of fluid in your body. Rare, but severe, complications include heart rhythm abnormalities, kidney failure, seizures, and even death.

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