Cannabis may be harmful to mental health. Experts explain why.

Cannabis has a longstanding reputation for helping people relax, but recent research has found it can have a negative impact on mental health. For that reason, it's understandable to have questions.

Cannabis — aka pot, weed or marijuana — is legal in 23 states, making it more accessible than ever. It’s also worth noting that many dispensaries sell strains of cannabis that are marketed as helping with certain mental conditions, including anxiety and depression. How are we to reconcile this contradictory information? Here’s a breakdown of the data, along with how mental health experts advise their patients on cannabis use.

What does the data say about mental health and cannabis use?

There have been a few studies about the impact of cannabis on mental health, and results have been mixed. Below are some of the major ones:

• A study of more than 6 million Danes published in JAMA Psychiatry in May found that people who have cannabis use disorder (meaning, they’re unable to stop using marijuana) had a higher risk of having psychotic and non-psychotic depression and bipolar disorder. The researchers found that people with cannabis use disorder had almost twice the risk of developing depression and an up to three times greater risk of bipolar disorder.
  

• A scientific review published in JAMA Psychiatry in 2016 found that people who use marijuana are more likely to develop temporary psychosis, as well as long-lasting mental disorders like schizophrenia. The link between schizophrenia and cannabis use was stronger in people who started using pot from a young age and continued to use it more frequently.
  

• A 2021 review published in Frontiers in Psychiatry notes that people with serious mental health conditions use cannabis “at rates much higher than the general population.” The lifetime cannabis-use rates for patients with schizophrenia, major depressive disorder or bipolar disorder are 80%, 17% and 24%, respectively, the review found. The researchers also found that about 40% of patients with schizophrenia and 20% of patients with major depressive disorder or bipolar disorder are also diagnosed with cannabis use disorder.
  

• On the positive side, a 2020 research article published in BMC Psychiatry concluded that there is "encouraging, albeit embryonic" (meaning, early stage) evidence for using medicinal cannabis to treat a range of psychiatric disorders. The researchers noted that there is “tentative support” for using CBD to treat social anxiety; there are also case studies that suggest cannabis may help with sleep and post-traumatic stress disorder. The researchers pointed out that cannabis may help with ADHD as well.
  

• Research has found that heavy marijuana use during the teen and young adult years can increase the risk of triggering the start of schizophrenia and psychosis. There is also evidence that regular marijuana use can speed up the start of symptoms of mood disorders like bipolar disorder and major depression, along with anxiety disorders — especially in younger people.

The National Alliance on Mental Illness (NAMI) notes that, while some states have legalized marijuana, it is still classified as a Schedule I drug, which makes it difficult to study. This has limited “robust scientific research,” NAMI says.

Mental health experts say the reality of cannabis use is complicated

A lot of the data around marijuana use and mental health focuses on people who are heavy pot users, making it difficult to say for certain how sporadic marijuana use will affect people, Hillary Ammon, a clinical psychologist at the Center for Anxiety & Women’s Emotional Wellness, tells Yahoo Life. It’s also difficult to say that heavy use of marijuana causes certain mental health symptoms — it may simply be that people experiencing certain mental health conditions are more likely to reach for marijuana.

“Studies show that frequent cannabis users consistently have a higher prevalence of anxiety and depressive disorders,” Dr. Zachary Kelm, clinical assistant professor in the department of psychiatry and behavioral health at the Ohio State University Wexner Medical Center, tells Yahoo Life. “At the same time, people with depression and anxiety are more likely to use cannabis. It is not clear whether cannabis use causes anxiety or depression, but there is clearly a relationship."

However, some people feel that cannabis use helps them to relax, Ammon says. “I work with a lot of clients with anxiety who have shared that smoking cannabis helps them feel calmer and slow down or quiet spiraling thoughts. Others report that it aids in providing better sleep at night,” she says. Ammon says she’s also worked with patients who have ADHD who say that some strains of cannabis help them focus.

“Anecdotal reports like that are hard to ignore,” Dr. David Nathan, a psychiatrist with Penn Medicine and Princeton House Behavioral Health, tells Yahoo Life. But Nathan says there are caveats. “Although people often like how they feel for the first few hours after they consume cannabis, it’s possible that they could feel a little more anxious or moody after cannabis is out of their system,” he says. “Using cannabis frequently could increase this kind of ‘rebound,’ and consumers might not make a connection between cannabis use and later negative effects.”

Developing cannabis use disorder is also a possibility when using marijuana, Kelm says. “Addiction, or cannabis use disorder, develops in about 10% of users,” he says. “Initiating cannabis at a younger age is a risk factor for developing problematic cannabis use, which can involve cravings, tolerance, withdrawal, difficulty cutting down on use, issues fulfilling major role obligations at work, school or home, use in physically hazardous situations and impairments in social or occupational functioning.”

What do experts recommend?

Experts generally recommend that people with mental health conditions try to avoid cannabis, particularly if they have a link to certain mental health disorders. “I almost always recommend that people with a personal history of schizophrenia or other psychotic disorder avoid THC-containing cannabis completely,” Nathan says. “Even people who have close relatives with psychotic disorders should think twice and exercise a lot of caution before using cannabis.”

Ammon also urges caution. “Cannabis use may be useful in the short-term, but it’s often just that — a temporary fix,” she says.“It may help you feel calm or quiet thoughts briefly, but those problems will often return.”

Kelm discourages its use too. “There is currently no strong scientific evidence that cannabis is a beneficial treatment for any mental health condition,” he says. “Cannabis use has been associated with both depression and anxiety, but it is not clear whether it causes these conditions.”

That said, Kelm says he keeps an open mind with patients who say that using cannabis helps their mental health. “We continue to work toward achieving their goals,” he says. “I also let patients know that I will continue to stay up to date on the scientific literature regarding cannabis and mental health as it evolves. We will hopefully have a better understanding of how cannabis, particularly THC and CBD, impacts both mental and physical health conditions over the next decade as more research is undertaken.”

If you want to try cannabis for mental health, Ammon suggests having a conversation with your health care provider first. “Speak with your medical provider about your interest and inquire if they support the use of medical cannabis and can provide a script,” she says. “Also, look into state regulations related to getting a medical cannabis prescription. The strains provided at these regulated stores are often cleaner and safer than drugs purchased from a non-regulated provider.”

Wellness, parenting, body image and more: Get to know the who behind the hoo with Yahoo Life's newsletter. Sign up here.