Why experts say the legalization of marijuana is no cause for celebration

Data should give policymakers pause as Congress considers further deregulating marijuana 

Last month, Senate Majority Leader Chuck Schumer, D-N.Y., introduced a bill to undo federal prohibitions on marijuana put in place when Congress made the drug illegal more than 50 years ago.

Attitudes toward cannabis use have fluctuated greatly in the last century. Banned in the ’30s, criminalized in the ’50s — cultural shifts led to more leniency in the ’60s. In the ’70s, then-President Richard Nixon rejected recommendations to decriminalize, though 11 states did independently.

The war on drugs brought the most severe punishments with growth in drug arrests. Eighty-two percent of arrests involved marijuana, although only 6% resulted in felony convictions. The approval of medical marijuana in California in 1996 initiated the trend toward legalization and now commercialization, leaving unresolved tensions between more liberal state policies and continued federal prohibition.

While a fresh look at federal policy could lead to greater uniformity when it comes to marijuana, studies continue to underscore the drug's harmful impacts. And, if the proposed legislation passes, an already expanded number of marijuana users in the country could further grow. Medical experts are asking policymakers to dispel the common misconception the drug is harmless and look to the data for how marijuana impacts the health and well-being of its users.

The data is anything but encouraging when it comes to the dangers associated with cannabis. “States for which there is rigorous data and for which enough time has passed since commercialization has been enacted are seeing a host of negative outcomes,” said Dr. Ken Winters, the founder of the Center for Adolescent Substance Abuse Research at the University of Minnesota.

Negative outcomes include research that suggests a connection between smoking marijuana and respiratory symptoms like chronic bronchitis. The drug also tends to impact school performance. “Since marijuana use impairs critical cognitive functions ... many students could be functioning at a cognitive level that is below their natural capability for considerable periods of time,” one review from the New England Journal of Medicine notes

And multiple studies also link marijuana use and violence. A National Institute of Health study found that “marijuana use during adolescence nearly doubles the risk for intimate partner violence;” and another study from Frontiers in Psychiatry suggests a “unidirectional association between cannabis use and violence.” Journalist Alex Berenson, author of the book “Tell Your Children: The Truth About Marijuana, Mental Illness and Violence,” documents the rising cases of mental illness in tandem with cannabis use.

The data is anything but encouraging when it comes to the dangers associated with cannabis.

The number of new users, meanwhile, and the frequency with which they use marijuana shows few signs of slowing. One study found that in 2006, about 3 million Americans reported using the drug at least 300 times a year, “the standard for daily use,” the study noted. But the same study showed that by 2017 the number of users who used the drug at least 300 times a year had more than doubled, increasing to 8 million, approaching the number of Americans who drink every day.

The number of casual users has also increased. In 2019, 48 million Americans reported using the drug at least once that year — accounting for nearly 18% of the country or 1 in 5 Americans. That year the U.S. surgeon general sounded a national alarm on the drug’s harmful effects, including on the developing brain and its link to psychotic disorders.

On that front, a study in The Lancet found that “the odds of psychotic disorder among daily cannabis users were 3.2 times higher than for never users.” And of course, marijuana can also be addictive. “Marijuana addiction is much more common than most people realize,” said Dr. Samuel Wilkinson, the associate director of the Yale Depression Research Program at Yale School of Medicine. “Large and reliable epidemiological studies suggest that about 1 in 3 marijuana users have some form of addiction.” 

Despite all the evidence, many advocates for its legalization still claim that cannabis is “relatively safe” or even “harmless;” coinciding with a growing number of Americans who believe that “using marijuana causes little to no harm” — an alarming and puzzling notion to public health officials. “If it were benign, nobody would use it,” neuroscientist Yasmin Hurd told The Harvard Gazette earlier this year. “Cannabis contains over 500 chemicals, including over 140 cannabinoids that have a greater or lesser degree of psycho-pharmacological activity.” 

To make matters worse, evidence suggests that such chemicals are becoming more potent, another source of concern among the experts I interviewed. “The biggest detriment of cannabis legalization in the U.S. in my mind has been the lack of regulations around high potency cannabis products,” explained Dr. Rosalie Liccardo Pacula, a health policy professor at the University of Southern California. “U.S. markets have the highest potency products available, and with these higher potency products we are seeing growing numbers of cannabis poisonings, cannabis hyperemesis syndrome, psychosis, pregnant women in the E.R., addiction, and cannabis-involved motor vehicle fatalities.” 

Winters said many such consequences could have been avoided if policymakers would have listened to early warnings from public health experts. “I cannot identify one harm or negative outcome predicted by health officials that has not come to be a reality,” he told me. 

Legalized marijuana, of course, has become a major source of tax revenue for some states. This, again, has created its own tricky kind of dependency. Any attempts to scale back could mean budget cuts. And then there’s also the issue of new business. “There have been some increases in new jobs,” said Pacula. Cutting jobs or tax revenue isn’t politically popular, even if some experts suggest that states may be worse off financially in the long run. “Tax revenues from marijuana sales do not cover the costs of added harms and health issues that communities have to bear,” said Winter.

Beyond quality control, tax revenue and employment opportunities, medicinal marijuana may hold some potential health benefits for people with certain medical conditions. It is an effective temporary treatment for multiple sclerosis symptoms, for example, and the American Cancer Society has acknowledged that cannabis “can be helpful in treating nausea and vomiting from cancer chemotherapy.” Some make the case for its use as pain treatment.

But experts told me that safer alternatives to marijuana are readily available and should be considered instead. “If we think we need some sort of cannabis constituent, I would favor using FDA-approved forms of it and avoiding smoked cannabis,” Wilkinson said. “I mean, how many other medicines do you know of that are smoked?” Smoking marijuana can cause respiratory issues, one of the reasons the American Lung Association specifically warns against it: “We caution the public against smoking marijuana because of the risks it poses to the lungs,” the organization notes.

“Large and reliable epidemiological studies suggest that about 1 in 3 marijuana users have some form of addiction.”

Jonathan Caulkins, a professor of operations research and public policy at Carnegie Mellon University’s Heinz College, offered a similar take: “Cannabis is directly useful for treating only a small number of things, and for most of those things there are better alternatives,” he said. 

Wilkinson also noted that some people have the perception that marijuana can be beneficial against depression and anxiety, “but mostly the objective data shows the opposite,” he said. “The trouble is that people often feel a transient reprieve when high but then tend to return to a worse baseline,” he explained. “This is not unlike saying that alcohol helps with depression or anxiety (which it can transiently), but the objective data is overwhelming that people with alcohol addiction and depression or anxiety feel worse than depressed patients without alcohol problems.” 

With the harms of legalization and commercialization seemingly outweighing benefits so significantly, many wonder how marijuana legislation has been able to pass so quickly and so broadly, especially with the aforementioned measures currently being considered in Congress to deregulate federal cannabis prohibition even further.

“Policy makers rallied around the mantra ‘we have to follow the science’ when it came to dealing with COVID-19,” Winters said, “yet the science on the health impacts of cannabis is so often ignored by them.” Indeed, a PubMed study points to “a shrewd and expensive lobbying campaign” making so many Americans tolerant of a drug that “presents more serious risks than most people realize.” 

Wilkenson said better testing and regulation are more important than ever. “Marijuana is unlike virtually every other ‘medicine’ in that it has not gone through rigorous clinical trials that are regulated by the Food and Drug Administration,” he explained. “Instead, state legislatures, using a variety of criteria, have somewhat arbitrarily decided that it can be used within their state boundaries as an ailment for various health disorders.” 

Beyond regulation and slowing down legalization efforts, health officials also want to improve messaging and education similar to what occurred when cigarettes were de-glamorized after being presented as “cool, cheap, legal and socially acceptable” throughout the mid-20th century. “We need sensible, evidence-based education on weed for all stakeholders, including young people and health care professionals,” Harvard Medical School’s Dr. Kevin Hill wrote for NBC News, “to bridge the gap between the science of cannabis and public perception.”