How good is marijuana for pain, sleep or anxiety? What the science really says

A recent analysis of over 100 clinical trials finds limited evidence supporting marijuana's health benefits, while pointing to potential harm, particularly for pregnant women and adolescents.

If you're one of the many people who are using or contemplating the use of marijuana to alleviate anxiety, pain, nausea, or sleep issues, you might want to take a closer look at the latest findings.

A recent analysis of over 100 relevant clinical trials and meta-analyses has concluded there is little high-quality evidence supporting the benefits of marijuana for various health problems. There is some limited evidence that cannabis helps with seizures, muscle spasms, chronic pain, and sleep — but only for certain patients.

Moreover, some of the more convincing evidence points to potential harm associated with cannabis use, including effects that negatively impact mental health. The people who are most at risk of being harmed by marijuana use are pregnant women (potential problems for babies) and adolescents (potential cognitive development issues).

Many people self-medicate using marijuana but may be unaware of risks

North America stands as the global leader in medical cannabis. In Canada, regulated medical cannabis use became legal in 2001, while the USA has 36 states that allow medical cannabis use. Notably, the Food and Drug Administration (FDA) has sanctioned four cannabinoid drugs for prescription use. The spectrum of medical conditions for which cannabis is approved varies, with epilepsy, cancer, and multiple sclerosis being common ones.

But the effectiveness and safety of marijuana for certain approved conditions remain questionable due to inadequate evidence. Studies on medical cannabis efficacy often lack randomized control comparisons, relying instead on small patient cohorts or case reports. Particularly, studies exploring cannabis as a treatment for anxiety often provide low-quality evidence with limited improvement in symptoms and substantial adverse effects.

This is important because many people claim they use marijuana for medical reasons, rather than recreational use. In 2022, researchers at the University of Queensland in Australia and the University of Waterloo in Canada found that, on average, 27% of Americans who used cannabis at least once did so for medical purposes. In US-legal recreational states, the prevalence of marijuana use as a medicine is 34%. The study involved more than 27,000 participants aged 16 to 65 years.

The most common physical health reasons for turning to marijuana include use to manage pain (53%), sleep (46%), headaches/migraines (35%), appetite (22%), and nausea/vomiting (21%). For mental health reasons, the most common were for anxiety (52%), depression (40%), and PTSD/trauma (17%). Nearly 11% of the participants reported using cannabis for managing other drug or alcohol use and 4% for psychosis.

In their latest review, the researchers led by Marco Solmi, a psychiatrist at the University of Ottawa, found there is little high-quality evidence in the current scientific literature supporting the benefits of marijuana for many of these health concerns. After meticulously applying strict quantitative criteria and considering both observational studies and clinical trials, the researchers found that most of the associations between cannabis use and health outcomes were supported by very low or low credibility evidence.

“The most concerning findings are the multidimensional detrimental effects of cannabis on brain function, as reflected by associations with poor cognition (and) mental disorders,” Solmi told CNN.

“If we pair these findings with the fact that almost 2/3 of those with mental disorders have onset before age 25, it sounds reasonable to state that cannabis should be avoided in younger strata of the population,” he said.

What are the potential dangers of marijuana use?

Interestingly, the study's most compelling findings didn't revolve around the potential benefits of marijuana, but rather the potential dangers.

While marijuana use is often touted as a quick fix for anxiety, depression, and many other mental disorders, the researchers found little evidence of such benefits. If anything, the opposite seems to be more likely.

The review found that patients who experience psychosis, a mental condition characterized by a disconnection from reality, can relapse and even worsen their condition by using cannabis. Psychosis is a common symptom among people with bipolar disorder, clinical depression, and schizophrenia.

Many pregnant women use cannabis to ease their nausea. The nausea-canceling effects of marijuana are owed to delta-9-tetrahydrocannabinol, or THC, the active cannabinoid in marijuana that is also responsible for the "high". But in doing so, there's a risk of having a smaller, low-birth-weight baby. A 2020 study by gynecologists at Queen’s University in Kingston concluded there is "no known safe level of cannabis use during pregnancy or lactation," adding that "[in] utero exposure to cannabis has been associated with long-term neurodevelopmental outcomes that persist into young adulthood." Pregnant mothers should stay clear of cannabis like they should avoid alcohol or tobacco.  

Concerning adolescents and young adults, there is compelling evidence that marijuana use may stunt cognition, language development, visual recall, and memory, as well as trigger mental health conditions. It is not known at the moment if these effects are reversible following cessation.

What about the potential medical benefits of cannabis?

Among the studies with better data, cannabidiol (CBD) has proven to be valuable in addressing epilepsy, while cannabis-based medicines have demonstrated potential for improving spasticity in individuals with multiple sclerosis. Moreover, cannabis can treat symptoms of chronic pain and help with sleep for those suffering from cancer-related sleep disturbances, the researchers found.

However, although cannabis appears to be effective in managing pain across various measures and populations, the study didn't find evidence supporting the notion that cannabis improves sleep in the general population.

Nevertheless, the researchers urge patients not to self-medicate and seek medical guidance before they decide to use cannabis for a particular ailment.

But perhaps the biggest finding is that there is still very much we don't know about cannabis and its consequences on our health, despite the fact that it is an herb used and cherished by millions. The researchers found very little high-quality evidence pointing to outcomes in either direction, positive or negative, which is why they call for a revision of current rules and regulations. Although cannabis is recreationally legal in many states, researchers who want to study cannabis need to jump through numerous hoops. If they work with cannabis directly, they need to get DEA approval and source their cannabis from a federally approved supplier.

Starting in 1968, U.S. researchers were allowed to use cannabis from only one domestic source: a facility based at the University of Mississippi, through a contract with the National Institute on Drug Abuse (NIDA). But since 2021, scientists have finally been allowed to source cannabis for their research from other approved crops. Hopefully, these developments will improve the number and quality of studies that focus on the medical effects of cannabis.

The review appeared in The British Medical Journal.

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