Federal approval for medical marijuana may be on the horizon. Following years of advocacy from cannabis supporters and the industry, the Trump administration is working to relax some restrictions and enhance research into the therapeutic benefits of the drug. Currently, medical marijuana is permitted in 40 U.S. states and Washington, D.C., for treating a range of conditions like arthritis, inflammatory bowel disease, hepatitis C, cancer, glaucoma, and Alzheimer’s. Yet, despite its widespread use, experts highlight that scientific evidence supporting its efficacy for many of these conditions remains limited, although there are promising findings.
“Some people will have you believe that it can help every condition,” says Jack Wilson, a postdoctoral research fellow at the Matilda Center for Research in Mental Health and Substance Use at the University of Sydney in Australia. “They think that it’s some sort of silver bullet, but that’s just not the case.”
Studying cannabis presents inherent challenges. The plant, Cannabis sativa, contains numerous compounds, including over 100 cannabinoids, each with potential health effects. Additionally, cannabis is consumed in various forms—like flowers, waxes, edibles, tinctures, creams, and suppositories—and in different dosages. Federally, cannabis has been categorized similarly to heroin and LSD, complicating and increasing the cost of research due to the need for extra permissions and security measures.
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There is also a shortage of clinical evidence. Many medical marijuana products on the market have not undergone large-scale clinical trials, which are essential for confirming the safety and effectiveness of treatments. “That’s why there’s so much confusion,” says Ryan Vandrey, a professor of psychiatry and behavioral sciences at Johns Hopkins University. “That’s why there’s such a lack of good clinical evidence.”
Despite this, people continue using marijuana medicinally. “Societally, people are moving on with this as a medicine with very little data,” says Margaret Haney, director of the Cannabis Research Laboratory at Columbia University. “People say, ‘Talk to your doctor.’ Well, your doctors don’t know anything because they don’t have the data.”
Scientific American consulted several cannabis researchers to explore which medical marijuana treatments are scientifically supported, what research areas hold promise, and how potential federal regulatory changes might address evidence gaps.
What does cannabis do to our body?
Consuming cannabis through smoking, vaping, or eating can affect the brain and body in various ways, including inducing relaxation or causing adverse reactions like increased anxiety or paranoia.
The psychoactive effects of cannabis are primarily due to the cannabinoid tetrahydrocannabinol (THC), which interacts with the endocannabinoid system—a network of neural pathways that helps regulate sleep, mood, and brain function. Cannabinol (CBD), another prevalent cannabinoid, also interacts with this system but in a less pronounced manner.
Factors such as the amount of cannabis consumed, an individual’s age and physiology, the form of cannabinoids in the drug, and the method of consumption all influence its effects. For instance, inhaling cannabis can cause immediate physiological effects, according to Igor Grant, a psychiatry professor at the University of California, San Diego. In contrast, consuming cannabis as an edible may delay the effects as it passes through the gastrointestinal tract.
What uses of medical marijuana are best supported by evidence?
Cannabis has been used medicinally since ancient times, with usage records dating back to 2800 B.C.E. in China. In the U.S. today, only a few medical cannabis products are FDA-approved. These include a CBD-based drug called Epidiolex, used to treat rare epilepsy forms in children, and three synthetic cannabinoid drugs for nausea in cancer patients and AIDS-related weight loss.
A 2017 report from the National Academies of Sciences, Engineering, and Medicine found the strongest evidence for cannabis’s medical use in treating chronic pain, chemotherapy-induced nausea, and symptoms related to multiple sclerosis.
Some findings are promising—but more research is needed
For other potential medical marijuana uses, the evidence is less clear.
A recent review by Wilson and colleagues found no evidence supporting cannabis in treating mental health conditions like anxiety, anorexia nervosa, or PTSD. Interestingly, the research suggested that medical marijuana might help treat cannabis use disorder, akin to how nicotine patches aid in quitting smoking.
Wilson emphasizes that the absence of evidence doesn’t mean research into these or other conditions should cease: “The door isn’t closed on a lot of these conditions,” he says. “We should definitely pursue more evidence.”
For instance, Grant mentions that colleagues at the University of California, Davis’s Center for Medicinal Cannabis Research are conducting a clinical trial suggesting CBD may alleviate some anxiety related to anorexia.
While not definitive, there is “increasing evidence” that CBD may help treat anxiety in some people, Grant notes. If proven true, this would be significant. CBD has a “pretty good safety profile,” potentially allowing those with anxiety to rely less on medications like antidepressants and benzodiazepines, which can have negative side effects or become addictive. Nonetheless, further research is necessary.
Preliminary evidence also indicates that CBD might treat schizophrenia with fewer side effects than antipsychotics, which can lead to weight gain and neurological issues, according to Grant.
Other research avenues include examining cannabinoids’ anti-inflammatory properties and the role of THC and CBD in managing metabolic syndrome, a precursor to heart disease, type 2 diabetes, and stroke.
How experts say a change in federal laws could help
In April, the Trump administration reclassified state-licensed medical marijuana under the Controlled Substances Act (CSA) from Schedule I—where drugs like heroin are placed—to Schedule III, which is considered less dangerous. The administration also plans to reclassify all cannabis to Schedule III, which wouldn’t legalize it but would reduce research barriers.
“The movement from Schedule I to Schedule III is really important because it opens a lot of research doors,” Johns Hopkins’ Vandrey notes. “It’s not that none of this research could be done before, but it moving to Schedule III makes it easier to do the research.”
Previously, cannabis had to be managed with the same caution as heroin at the federal level, requiring extensive paperwork and strict storage and usage protocols.
“To study cannabis as a Schedule I drug, I have a gun safe in a locked room that the [Drug Enforcement Agency] approves and that only I can get in with my fingerprints,” explains Columbia’s Haney. Reclassifying cannabis could significantly increase the number of researchers studying it, she says, potentially accelerating much-needed clinical research.
“Right now we have the notion of medical cannabis really being driven by the industry,” Haney observes. “They’re running the narrative here because science cannot keep up with what needs to be done.”
