Marijuana has been legalized in some capacity in 31 U.S. states, in large office due to a softening opinion effectually the potential harms of the drug and recognition of its medical benefits. Equally a issue, cannabis has become the nigh unremarkably used illicit drug during pregnancy.

One recent study revealed that in 2016 seven per centum of pregnant women in California used marijuana, with rates as high every bit 22 percent amidst teenage mothers. In Colorado 69 percent of dispensaries recommended the drug to pregnant women to help with morning sickness.

Whereas marijuana is not a major health hazard for most adults, prenatal drug exposure can exist harmful to unborn babies. Previous research has shown infants exposed to cannabis in the womb are 50 pct more likely to have a lower birth weight. Now three new studies presented in November at the Society for Neuroscience almanac meeting in San Diego advise prenatal cannabis exposure—at least in rodents—could have serious consequences for fetal brain development. "There'south become this relaxation—in function considering [marijuana] is becoming legal in many states around the country—that it's fine," says Yasmin Hurd, who is director of the Addiction Institute at the Icahn Schoolhouse of Medicine at Mountain Sinai and was not involved in the new research. But, she adds, merely because a drug is non very dangerous to adults does non mean it is harmless to the developing brain.

In one study researchers at Washington Country University in Pullman showed rat pups born to mothers exposed to high amounts of cannabis vapor during pregnancy had trouble with cerebral flexibility. Twice a day the scientists filled the significant rats' containers with marijuana vapor from an e-cigarette, elevating levels of the psychoactive chemical THC (tetrahydrocannabinol) in the rats' blood to roughly the human equivalent of smoking a articulation. Subsequently the pups grew up the researchers trained them on a task that measured their ability to think flexibly and larn new rules. The young rats first learned to follow a lite cue to push 1 of ii levers in society to receive a sugary treat. The next day, pushing only the left lever would evangelize the advantage, regardless of which side the lite had been on.

The rats exposed to cannabis in utero learned the kickoff rule (following the calorie-free cue) without a problem, but they took significantly longer to acquire the new rule (pushing the left lever) than did rats not exposed to the drug. The cannabis-exposed rats also made many more mistakes on the second day. They would reply correctly for a couple rounds, making it seem like they knew the new rule, but so they would press the wrong lever again. "It was like something wasn't really clicking with them," says Ryan McLaughlin, an assistant professor of integrative physiology and neuroscience at Washington Land and lead author of the study, which has not nonetheless been published. He says they never got that "'Aha!' moment, where it's similar, 'Oh, this is what I'm supposed to practise.'"

In a similar written report, scientists at Auburn University in Alabama plant rats born to mothers that had been injected with a low, continuous dose of constructed cannabis during pregnancy were significantly impaired on several different retention tasks involving mazes. "The rats that were exposed to cannabinoids [chemicals like those plant in marijuana] prenatally were performing less efficiently than the control rats" that were non exposed, says Priyanka Pinky, a graduate pupil at Auburn who conducted the research. "There was a gap in the acquisition of the memory and the consolidation of the memory."

The young rats whose mothers were dosed with the drug also had abnormalities in the hippocampus, the encephalon's primary memory centre. Specifically, they had difficulty creating new connections betwixt neurons—the ground for forming new memories. The researchers recollect the differences in the hippocampus stem from changes in levels of glutamate, the brain's master excitatory neurochemical involved in learning and memory.

In the third study researchers at the University of Maryland School of Medicine and the University of Ferrara in Italian republic again establish impairments in retention and changes in levels of glutamate in the brains of rats exposed to THC in the womb. They as well discovered an increase in another molecule in the brain, which they think may be the missing link betwixt prenatal cannabis exposure, glutamate and cerebral impairments: kynurenic acid. This chemic acts like a puppet primary in the brain, regulating glutamate and other important neurochemicals; high levels of the molecule result in lower glutamate levels. Kynurenic acid has also previously been implicated in cognitive impairments in both people and animals.

"We think that prenatal marijuana exposure tin can induce an increase in kynurenic acrid, and this may exist responsible for the cognitive impairment observed in the offspring of marijuana users," says Sarah Beggiato, a postdoctoral researcher at the University of Ferrara in Italian republic and co-writer of the study. "Why is glutamate going down? Information technology's considering kynurenic acid is going up." The scientists are now researching drugs that block the acid's synthesis, which may help defend against the problems associated with prenatal cannabis exposure.

The findings, which are in rodents, may not necessarily interpret to humans. Mount Sinai'southward Hurd, who has been researching the furnishings of marijuana on the developing encephalon in both humans and animals for 15 years, says the new studies do not reveal anything "shockingly new." But they evidence "that in that location are indeed multiple systems being affected," she says, "and given that more pregnant women today are starting to smoke marijuana, information technology'south really important for us to get that word out."