Some of my friends are having babies, and some of my friends smoke weed. Sometimes, they do both — and not long ago, one friend asked me if it was safe to smoke while pregnant.
I had to look it up, so I told her I’d get back to her the next day. It took me a lot longer: On what I thought would be a quick search of a medical sciences literature database, I found a pile of research on the subject — as of press time, in fact, exactly 420 scientific papers on cannabis-related pregnancy outcomes. Even more surprisingly, these studies pointed in a few different directions — they didn’t circle around one unambiguous truth, and in fact, many contradicted each other.
Then I found something even more startling: Many states, including ones where weed is legal, harshly punish Americans for using cannabis during pregnancy, often by allowing courts and child welfare agencies to charge parents with child abuse or neglect. Additionally, many states — not necessarily the same ones — have policies requiring that health care providers report drug use in pregnant people when they diagnose it.
Cannabis is only one of many drugs for which these punitive policies exist: They also apply to a range of other substances, including cocaine, methamphetamine, and opioids. But more pregnant people use cannabis than any of these other drugs, especially as states have increasingly legalized its sale and use.
But it’s the larger-scale effects of these policies that might be the most damaging: By deputizing pregnancy health care providers as an arm of the law, they create a climate of fear and distrust between prenatal health care providers and patients.
These are the very places where pregnant people would ideally be learning how to minimize the harm drug use could do to their pregnancies. Yet both patients and providers have incentives to never mention it — and fear of being caught might lead patients to avoid care altogether.
The more I read, the more I wondered: How did we get here? And how can we do better?
Cannabis effects on human fetuses are plausible but hard to prove
People use cannabis during pregnancy for a variety of reasons.
Most are trying to manage pregnancy symptoms, most commonly nausea and vomiting, which about 70 percent of pregnant people have said is their reason for using cannabis. Other symptoms people treat with the drug include anxiety, pain, headaches, cramping, sleep disturbances, and low appetite.
Cannabis use during pregnancy wouldn’t be a concern if it didn’t expose the growing fetus to a substance that could theoretically cause it harm. Unfortunately, it does.
During a pregnancy, the fetus gets nutrients and oxygen from the parent’s blood — but only after it’s been filtered through the placenta, a temporary organ that grows alongside the fetus inside the womb (and leaves the womb along with the fetus during delivery). When a pregnant person uses marijuana, their fetus’s bloodstream probably has anywhere from 2.5 to 6 times less tetrahydrocannabinol (THC), the major psychoactive compound in cannabis, than theirs.
Along with THC, more than 100 different compounds in cannabis exert a range of effects via the endocannabinoid system, a set of neurotransmitters and their receptors scattered throughout human and animal bodies, including (but not limited to) their brains. Within that system, cannabis compounds mimic the naturally occurring neurotransmitters that the receptors normally recognize.
Scientists have found that in animals, the wiring of that system evolves differently in a fetus’s developing brain if it’s exposed to cannabis in utero. In rats, those differences translate into behavioral differences in babies born to cannabis-exposed rat moms: They’re more anxious; they’re less sociable; they don’t remember or learn or pay attention as well as other rats; they’re potentially more prone to opioid dependence.
“There’s just a lot of biologic plausibility there, that as the brain is developing and you’re developing all of these different receptors, that being exposed to a substance like this would affect those areas of the brain and development,” said Katrina Mark, an OB-GYN at the University of Maryland who specializes in the care of people with substance use disorders.
But plausibility isn’t proof — and for decades, scientists have been studying children exposed to cannabis in utero to try to understand what’s actually happening.
It’s not the ideal way to get an answer to a scientific question about what effects a particular drug causes during pregnancy. In a world without bioethics, researchers with these kinds of questions could do a trial where pregnant people are randomly selected to either take the drug or not, then compare outcomes in babies born to each group. But because there’s reasonable suspicion that cannabis could cause harm — and because it’s illegal at the federal level — that’s not a study researchers can conduct in humans.
Instead, scientists are stuck with observational studies, in which they literally observe what happens among babies born to people who choose to use cannabis. Those can be informative, but they’re not perfect. People who use cannabis while pregnant might be different in important ways from people who don’t. It’s hard to know from these studies if it’s the weed, or a correlated factor — mental health, anxiety, demographics — that would account for any differences between their children.
What the data actually says
So what do these observational studies say?
Much of the data on cannabis’s effects on fetuses during pregnancy comes from three big observational studies that followed children born to mothers between 1982 and 2006. Children born to mothers who’d used cannabis had differences that varied with age: Toddlers had decreased memory, poorer sleep, and decreased attention; 6-year-olds had decreased attention, increased hyperactivity and impulsivity, and decreased concentration; and preteens and teens had poorer concentration and verbal reasoning, more depression, and more delinquency.
Many other, smaller studies have been conducted since — but none have escaped the problems that come with conducting observational studies. In a 2020 review of relevant studies published since the mid-1980s, the authors called out many of these studies for weak methodology. In particular, many researchers had failed to compare the outcomes they were measuring against any kind of a standard that would account for age and parental educational level. (That is: What if the kids of those who used cannabis during pregnancy were born to parents with lower levels of education, which could account for some differences?)
The review authors concluded that overall, “prenatal cannabis exposure is associated with few effects on the cognitive functioning of offspring.” What’s more, they noted, even when abnormalities were identified, almost all were still within the range of normal.
Mark said the problems with many studies’ design stem from the biases many researchers bring to the table. “If you look at studies of pharmaceuticals, they start from a place of innocent until proven guilty, whereas illicit substances are guilty until proven innocent,” she said. “So I think we’re sort of preprogrammed to think that there’s going to be harm.”
Cannabis can be safer than some alternatives
Despite the imperfect data, Mark suspects the risk of fetal harm with prenatal cannabis use is high enough to support recommending against purely recreational use.
But many aren’t seeking to get high. For three years, Shonitria Anthony has hosted Blunt Blowin’ Mama, a podcast and online community aimed at normalizing moms who smoke weed. In that time, she said, not one single mother has told her she’s smoking during pregnancy just to get high. “If anything, they’re scared to get high,” she said. “They’re wondering how much is too much.” She says they’re mostly looking to use the smallest amount they can get away with while managing their symptoms, like nausea and pain.
But here, things get trickier.
The American College of Obstetricians and Gynecologists recommends doctors counsel pregnant patients against using cannabis in favor of an alternative. But in many cases, physicians simply say, “Cannabis is risky, so don’t use it,” said Mark.
Yes, cannabis might come with some risks. But it’s possible those risks aren’t as bad as the alternatives.
Let’s say a pregnant person is using cannabis as their anti-nausea medicine. If their doctor tells them to stop using it, the alternative might be they just remain too nauseous to eat. That comes with its own risks; growing fetuses need nutrition.
Or let’s say they are using cannabis to manage pain. “If they’re using it for pain and their alternative is to use opioids,” which cause a range of negative effects on fetuses, “we have to reframe the conversation,” said Mark. In those situations, we have to ask: Which is going to cause less harm? The answer might reasonably be cannabis. (Although a pregnant person ideally would not consider using prescription opioids, nearly 7 percent of pregnant people do, and 1 in 5 of them misuse the drugs.)
Legal pharmaceuticals are sometimes an option for managing pregnancy-related symptoms. But there are risks and unknowns here, too. The vast majority of medications haven’t been assessed for their safety in pregnancy. So the selection of known safe options is small.
Arguably, even the legal drugs that have been evaluated for safety have been studied far less rigorously than cannabis has over the years. “There is a bigger evidence base for that neurocognitive development from cannabis exposure than there is from the medications we prescribe,” said Mishka Terplan, an OB-GYN and addiction medicine doctor who is now a research scientist at Friends Research Institute.
For patients who place their trust in the products with the biggest evidence base, cannabis may seem a far safer choice than some pharmaceuticals.
Despite the soft science on prenatal cannabis, it’s punished in severe and confusing ways
Although the science linking prenatal cannabis use to pregnancy outcomes is far from settled, a lot of US state law punishes people pretty severely for using the drug while pregnant.
About half of states consider any substance use during pregnancy equivalent to child abuse — including cannabis, regardless of whether it’s legal for recreational or medicinal use in that state. Three also consider it grounds for involuntary admission into drug rehab, and three consider it grounds for criminal prosecution — which means people found using drugs while pregnant can end up in jail. Since these policies first entered the legislative vocabulary in the mid-1970s, the punishments they’ve carried have fallen disproportionately on Black people.
There’s also an immensely confusing thicket of policies around testing for and reporting prenatal drug use. A range of state policies require health care providers to test and/or report pregnant people or newborns for drug use or exposure when they suspect it.
Hospitals can also make their own protocols for testing and reporting — and while they have to follow state law on what to do with the information they obtain, they can report parental drug use to child welfare agencies even when the state doesn’t require it. And while parents cannot be tested for drugs without their consent, newborns can. If a baby tests positive for a drug — and yes, a baby’s poop, urine, and blood can test positive for cannabis — state policy related to that substance gets applied to the parent.
Even in states where there aren’t laws on the books specifically targeting prenatal drug use, prosecutors do sometimes bring cases against people who use drugs during pregnancy.
All these punitive policies adds up to an incredibly confusing environment for both patients and providers, said Mark. That leads providers to simply avoid asking and talking about cannabis use during encounters in the clinic.
That confusion translates into several realities that end up being bad for both babies and parents. For starters, it means health care providers are often so confused about what they can, should, and must do if they learn a pregnant patient is using cannabis that they just avoid the subject altogether. “A lot of medical practitioners don’t really face the cannabis issue head on with patients and they just sort of try not to talk about it,” said Mark, “because they’re either uninformed or they’re not sure what they’re allowed to say.”
But especially concerning are the effects the policies have on pregnant patients. Instead of leading pregnant people to stop using drugs, punitive drug policies lead them to avoid seeking prenatal care, likely because those are the settings where they’d be identified as using drugs.
“When people worry that they are going to lose their babies if they go to the doctor while they’re pregnant and using drugs, or [if] their health provider finds out that they’re using drugs, they avoid care,” said Sarah Roberts, an epidemiologist at the University of California San Francisco who studies policies around substance use in pregnancy. That limits options for providing them not only with support aimed at reducing substance use, but also for linking them with nutrition, housing, and other health care.
In contrast to the consequences of cannabis use, the results of inadequate prenatal care are unambiguously negative: The risk of low birth weight and infant death is several times higher in pregnancies that don’t receive prenatal care, and both infant and maternal harms from preventable causes like diabetes and preeclampsia can be reduced with care that starts early in a pregnancy.
In states with punitive policies related to prenatal substance use, more pregnant people overdose on opioids, fewer get treatment for substance use disorders, and more infants are born with opioid-related and other complications, like prematurity and low birth weight.
Why do we do this?
The US is an outlier among nations when it comes to punishing drug use in pregnancy, and the negative effects of its punitive approach fall disproportionately on racial and ethnic minorities, especially indigenous and Black people. Furthermore, although a variety of laws punish pregnant people for exposing a fetus to drugs, there are no similar laws related to tobacco — despite a much higher level of evidence linking tobacco use in pregnancy with lung problems and congenital anomalies in newborns.
All of this suggests these policies represent the long shadow of the nation’s fraught history with drugs.
“Nixon’s war on drugs ... really made us look at drug use as a moral failing and a legal problem more than a medical problem,” said Mark.
Moral panics have motivated lots of policies around drugs and pregnancy in the US — and enough time has since passed that we should be able to learn from the events that followed. A key example is the 1990s’ national freakout about crack babies — a supposed epidemic of children born with disabilities due to in utero exposure to a type of cocaine. Although it ultimately turned out prenatal crack cocaine exposure had little to no developmental consequences, separating children from mothers due to positive drug tests did immeasurable harm to children and parents, and disproportionately traumatized Black families.
But generally, moral panic around cannabis is receding in the US. It’s more acceptable in many aspects of life and, increasingly often, legal. Why is pregnancy insulated from the normalization and acceptance of this drug in so many other parts of American society?
“The policy is not motivated by science,” said Terplan. “It’s not motivated by population health,” he said. Which feels uncomfortably familiar: So many policies relating to reproductive health, and the decisions people make during pregnancy, have nothing to do with well-being. They’re about control.