It’s no secret that marijuana legalization policies — both medical marijuana and recreational — have taken place with little to no research into the health effects of this drug. Last week, the National Academies of Sciences, Engineering, and Medicine (NAS) issued a report that called for more research into marijuana, or cannabis, as the plant is called.

In addition to recommending more research on the beneficial and harmful effects of cannabis and cannabinoid use, the committee emphasized that having cannabis on Schedule I of the Controlled Substances Act, the category reserved for drugs with high abuse potential and no accepted medical use in the United States, makes it extremely difficult to conduct research. They added that a diverse network of funders is needed to support research into cannabis and cannabinoids.

The NAS committee that wrote the report looked at more than 10,000 abstracts to reach almost 100 conclusions. The abstracts included information on the therapeutic effects of cannabis, as well as risks of cancer, mental health disorders and other diseases.

“For years the landscape of marijuana use has been rapidly shifting as more and more states are legalizing cannabis for the treatment of medical conditions and recreational use,” said Marie McCormick, chair of the NAS committee. “This growing acceptance, accessibility, and use of cannabis and its derivatives have raised important public health concerns,” said McCormick, who is the Sumner and Esther Feldberg Professor of Maternal and Child Health in the Department of Social and Behavioral Sciences at the Harvard T.H. Chan School of Public Health; and professor of pediatrics at Harvard Medical School. “Moreover, the lack of any aggregated knowledge of cannabis-related health effects has led to uncertainty about what, if any, are the harms or benefits from its use.”

Marijuana is the most popular illicit drug in the United States, in terms of regular (past-month) users. Based on a recent nationwide survey, 22.2 million Americans ages 12 and older reported using cannabis in the past 30 days; 90 percent of adult users said their primary use was recreational and 10 percent medical only, while 36 percent reported a mix of recreational and medical use. Between 2002 and 2015, the percentage of past-month cannabis users in the U.S. population ages 12 and older has increased steadily from 6.2 percent to 8.3 percent.

Therapeutic uses of medical marijuana include treating chronic pain in adults. Medications made from synthetic cannabinoids have been shown to reduce spasms in multiple sclerosis and prevent and treat chemotherapy-induced nausea and vomiting in adults.

Risks include being in a motor vehicle accident. For children, there is an increased risk of unintentional overdose injuries in states where marijuana is legal, with ingesting the most common route. One study found that from 2000 to 2013, the annual rate of poison center calls related to cannabis exposures among children younger than 6 years of age was 2.82 times higher in states that had legalized medical cannabis prior to 2000 than in states where medical cannabis remained illegal as of 2013. The committee called for more research to determine whether and how cannabis use is associated with death or with occupational injury.

In particular, there is evidence that cannabis use can increase the risk of developing schizophrenia and other psychoses, as well as social anxiety disorders, according to the report. To a lesser extent, it may also increase the risk of depression. However, in individuals who have psychoses, marijuana may be linked to better performance on learning and memory tasks.

There is also evidence that the more frequently someone uses cannabis, the more likely they are to develop “problem cannabis use.”

The committee found that learning, memory and attention are impaired after immediate cannabis use. The evidence of impairments in cognitive domains is “limited,” as is evidence suggesting that cannabis use is linked to subsequent impairments in academic achievement and social roles.

However, there was specific concern about young people. “Adolescence and young adulthood are when most youth begin to experiment with substances of abuse, including cannabis, and it is during these periods that the neural layers that underlie the development of cognition are most active,” the committee wrote.

Evidence suggests that smoking marijuana during pregnancy is linked to lower birth weight, but evidence on other pregnancy and childhood outcomes is unclear.

The study was sponsored by the Alaska Mental Health Trust Authority, Arizona Department of Health Services, California Department of Public Health, Centers for Disease Control and Prevention (CDC), CDC Foundation, U.S. Food and Drug Administration, Mat-Su Health Foundation, National Highway Traffic Safety Administration, National Institutes of Health National Cancer Institute, National Institutes of Health National Institute on Drug Abuse, Oregon Health Authority, Robert W. Woodruff Foundation, Colorado Health Foundation, Truth Initiative and Washington State Department of Health.

For the report, which is available as a free download or for purchase in print, go to