Expectant mothers who smoke pot in pregnancy could increase their baby's risk for mental or emotional problems later in childhood, a new study finds.
Marijuana use during pregnancy was associated with a host of problems in the preteen years, researchers report.
Children exposed to pot in the womb were more likely to experience internalizing disorders such as depression and anxiety, as well as externalizing disorders such as lashing out at others or ADHD, researchers found.
These kids also were more likely to have problems socializing with others and sleeping well, and were at greater risk of mental problems like schizophrenia or obsessive-compulsive disorder.
These risks held firm even after researchers accounted for other risk factors such as home life and family history of mental or emotional problems, said lead researcher Ryan Bogdan. He's an associate professor of psychological and brain sciences at Washington University in St. Louis.
"They are small associations," Bogdan said. "They're not whopping large effects that are going to increase the likelihood that children are going to be experiencing these problems by twofold or anything like that. But they exist beyond these confounding variables."
Also, among the kids studied, a mom's pot use during pregnancy -- however small -- influenced the course of a child's development more than either alcohol or tobacco use, which also were considered, Bogdan added.
"The effects of marijuana in this data set were much larger and more consistent than the effects of alcohol or tobacco use," Bogdan said.
This is cause for concern because marijuana is often seen as a legitimate means of treating medical problems like morning sickness, said Patricia Aussem, associate vice president of consumer clinical content development for the Partnership to End Addiction.
"While some pregnant women may be using marijuana for recreational purposes or to address nausea and vomiting, exposure to the substance during pregnancy can adversely impact the developing fetus," said Aussem, who wasn't part of the study. "If help is needed for nausea, pain, sleep or other problems, the best course of action is to discuss it with their health care provider and follow recommendations that are known to be safe during pregnancy."
The study was published Sept. 23 in JAMA Psychiatry. Bogdan and his university colleagues evaluated data on children born between 2005 and 2009 to nearly 10,000 mothers across the United States. These kids have been studied since before birth, as part of the Adolescent Brain Cognitive Development Study.
The researchers compared how kids fared if their mom kept using pot after learning she was pregnant against kids whose mom either never used marijuana or stopped during pregnancy.
Pot use during pregnancy was associated with a host of mental, emotional and behavioral problems tracked by widely used screening tools like the Child Behavior Checklist, researchers said.
It could be that the chemicals in marijuana interact with the fetus in ways that alter a child's later brain development, Bogdan said.
Bogdan noted that the body's endocannabinoid system -- the brain receptors that respond to THC, the chemical in pot that causes intoxication -- is not expressed until around six weeks after conception in humans.
"That is roughly around the time that most mothers in the study learned they were pregnant," Bogdan said. Moms who kept using pot exposed those newly formed brain receptors to THC, potentially altering the course of development, he said.
But because this was an observational study, it's also possible that other factors related to marijuana use or developmental problems could be to blame, Bogdan added.
Outside factors could include the parents' genetics; their family history of mood or mental problems; prenatal vitamin use, or kids born early or with low birth weight.
Regardless, Bogdan said he would urge expecting moms to not use pot until more is known about the risks involved.
"These findings really suggest that clinicians and dispensaries should discourage use among women who are pregnant or even considering becoming pregnant," Bogdan said. "These data and the potential impact of prenatal cannabis exposure on offspring, I think, gives us concern about the safety of cannabis use during pregnancy."
"There are many studies indicating that prenatal cannabis use can cause problems including low birth weight, impulsivity, problems with attention span and the ability to learn," Aussem said. "Just as with nicotine, alcohol and other substances, pregnant women should avoid marijuana use throughout their pregnancy."
The U.S. Surgeon General has more about marijuana use and the developing brain.