Marijuana is the most widely used illicit drug during pregnancy, and despite frequent warnings from health experts, it is not healthy for the developing fetus.

Authorities from the National Institute on Drug Abuse voiced concern in a JAMA opinion piece this week about the skyrocketing number of women using the drug. The letter comes on the heels of a December report that showed a shocking 62 percent increase since 2002 in pregnant women who use marijuana.

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And there’s a strong likelihood that number is outdated — the data was only available through 2014. More states have legalized the Schedule I drug since then, both for recreational and medicinal purposes. The drug also continues to be promoted as a way women can manage morning sickness.

Related: Expectant Moms on Marijuana: Seriously?

“While the effects of marijuana on human prenatal development [are] limited at this point, research does suggest there is cause for concern,” the researchers stated. They advise women to avoid using marijuana or any other cannabinoids during pregnancy.

Babies born to mothers who use pot during their pregnancy are more at risk for a number of issues, including a lower IQ, decreased spatial reasoning, learning and memory problems, anemia, lower birth weights, and potential placement in neonatal intensive care. These babies are ultimately more at risk for suicide and drug use later in life as well.

“Tens of thousands of peer-reviewed articles tell us that marijuana use can produce serious health and social problems.”

The physicians state that while more studies need to be done to clearly define the risk of marijuana to infants and adults, expectant parents need to be aware of the risks. This is true especially as marijuana legalization is pushed across the nation and use is promoted as “no big deal.”

The warnings are echoed by the American College of Obstetricians and Gynecologists and the American Medical Association, among others. Currently, 29 states and Washington, D.C., have passed laws to legalize medical marijuana.

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The National Academy of Sciences also released a landmark report this week by top scientists on the health effects of cannabis and cannabinoids. After reviewing over 10,000 peer-reviewed academic articles, the scientists report marijuana use is connected to, among other problems: respiratory problems; mental health issues (such as psychosis, social anxiety, and thoughts of suicide); increased risk of car accidents; progression to and dependence on other drugs, including cocaine and heroin; learning, memory, and attention loss (possibly permanent in some cases); and low birth weight.

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As the report also stated, “In states where cannabis use is legal, there is increased risk of unintentional cannabis overdose injuries among children.”

“This report is a wake-up call to all Americans who have been sold the false promise that marijuana use is not harmful across multiple health outcomes,” Kevin A. Sabet, Ph.D., president of Smart Approaches to Marijuana (SAM), said in a statement.

Related: The Heavy Price of Persistent Pot Smoking

“It confirms that although more research is badly needed, tens of thousands of peer-reviewed articles tell us today that marijuana use can produce serious health and social problems. We should be doing everything we can to stop the marijuana industry from continuing to deceive the public the same way Big Tobacco did for a century.”