Is it dangerous to smoke weed? What you need to know about using marijuana.

The push to legalize marijuana at the federal level has gained ground ever since California legalized it for medical use nearly 30 years ago. Recreational marijuana is now permissible in 24 states and Washington, D.C. Only four states still outlaw marijuana with no medical exceptions. 

In 2022, President Joe Biden ordered a review of the drug's status as a Schedule I substance, which denotes that a drug has no accepted medical use and has high potential for abuse. If marijuana is reclassified, a renewed push for national legalization will surely follow. 

We aren't here to tell you whether to vote for or against legalizing marijuana. But as a doctor and mental health professional, we're concerned that many Americans may come away from this legalization push with a belief that marijuana is harmless − if not healthful.

That's not quite right, as a growing body of scientific literature shows, including a new landmark study in the Journal of the American Heart Association.

Marijuana can help relieve symptoms of illness

Let's be fair: Marijuana has been shown to alleviate the symptoms and side effects of certain conditions.

Scientific research suggests that the drug can reduce vomiting and nausea in patients undergoing chemotherapy, reduce muscle spasms in patients with multiple sclerosis and provide short-term relief for adults with chronic pain. 

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There's some evidence that marijuana might reduce tics in people with Tourette syndrome, increase appetite and reduce weight loss in people with HIV and improve sleep quality for people with sleep apnea. 

But because medical marijuana is federally illegal, there have been relatively few comprehensive and scientifically rigorous studies on its potential benefits. All these areas require further research, including whether benefits actually outweigh risks. 

And let's not get suckered into the cannabis industry's focus on medical utility. For the majority of users, marijuana is a recreational drug that brings pleasure, pure and simple.

Risks of marijuana use include heart attacks and strokes

Unfortunately, that's not all it brings. The risks are real. 

An American Heart Association study analyzed data from more than 430,000 adults collected over four years. Researchers found that marijuana use is linked to a significantly higher risk of heart attack and stroke, with the risk increasing with frequency of use. Daily users had a 25% higher chance of heart attack and a 42% higher chance of stroke than non-users. And the increased danger exists whether users smoke, vape or eat their cannabis products. 

It's also important to note that thanks to advances in agricultural technology, the potency of marijuana's psychoactive ingredient – tetrahydrocannabinol, or THC − has dramatically increased. 

Today's marijuana is nothing like the flowers and leaves that filled the joints smoked at Woodstock in 1969. At that time, marijuana contained less than 2% THC. By the '90s, that had doubled to about 4%. Today, THC content in the most popular strains of weed falls between 17% and 28%. Concentrated oils or "dabs," meanwhile, can contain upwards of 95% concentration.

The higher the potency, the greater the risk of addiction − despite the common misconception that marijuana is not addictive.

Not your grandma's weed:Why potency limits must be part of any push to legalize cannabis

A 2014 study from the New England Journal of Medicine showed that nearly 10% of people who try out marijuana get hooked. That figure increases to 17% among those who first try weed in adolescence and to 25% among those who get high every day. 

Marijuana is not a harmless substance, especially for adolescents whose brains have yet to fully develop. Yet teenage marijuana use is also at its highest level this century. 

Nearly 80% of cannabis users try the drug for the first time as a teenager. In the years following its legalization in Colorado via a 2012 referendum, marijuana use among 12- to 17-year-olds increased 65%.

Using marijuana at a young age can have lifelong consequences. The drug interferes with the development of the brain. Impaired attention, problems with memory and difficulty learning are all potential side effects of early exposure to marijuana. 

Studies have shown that frequent marijuana use can fundamentally alter the brain's prefrontal cortex (our brain's "personality center"), the cerebellum (which controls movement and balance) and the amygdala (which processes emotions and memories).

Recognition of the mental health risks of marijuana use is also growing. A six-year study found that teenage girls are five times more likely to develop depression or anxiety if they smoke weed every day. Because many use marijuana as a coping mechanism for anxiety and depression, they can get themselves into a vicious cycle of dependency and worsening mental health.

Recent research from the National Institutes of Health has linked cannabis use disorder − which afflicts more than 1 in 5 users − to an increased risk of developing schizophrenia.Among men in their 20s, as many as 30% of schizophrenia cases would have been prevented but for marijuana use.

Once people get hooked, marijuana can be incredibly difficult to quit. Withdrawal symptoms include depression, insomnia, anger, irritability and, of course, intense cravings to get high again.

Against all this data, it's a dangerous folly to think that getting high poses no health risks. 

At a time when social acceptance of marijuana and access to the drug have skyrocketed, even as youth mental health indicators are plummeting, it's more important than ever to reexamine the notion that weed is harmless. 

Phil McGraw, Ph.D., of daytime TV's "Dr. Phil," is one of the most well-known mental health professionals in the world and founder of Merit Street Media cable network, where he hosts "Dr. Phil Primetime." Dr. John Whyte is chief medical officer of WebMD.