Cannabis and Pregnancy: Risks, Research, and What Doctors Say

Cannabis use during pregnancy has become an increasingly common and increasingly complicated topic. As legalization expands and cultural attitudes toward cannabis shift, more pregnant individuals are considering or actively using cannabis products — often for the very real symptoms of pregnancy like nausea, anxiety, and insomnia. National survey data show that past-month cannabis use among pregnant women in the United States more than doubled from 3.4% in 2002–2003 to 7.0% in 2016–2017. Rates are highest in the first trimester, when morning sickness is most severe: use rose from 5.7% to 12.1% over the same period.

Yet major medical and public health bodies, including the American College of Obstetricians and Gynecologists (ACOG), the CDC, and the FDA, recommend against cannabis use during pregnancy and breastfeeding. This article presents the current state of the evidence as objectively as possible, explaining what researchers know, what they do not yet know, and why the medical consensus errs strongly on the side of caution.

Current medical consensus on cannabis and pregnancy

The position of the medical establishment is clear and unified: pregnant and breastfeeding individuals should not use cannabis in any form. This recommendation comes from the American College of Obstetricians and Gynecologists (ACOG), the American Academy of Pediatrics (AAP), the Society of Obstetricians and Gynaecologists of Canada (SOGC), the U.S. Surgeon General, and the FDA. These organizations base their recommendations on the precautionary principle — when the potential risk involves a developing fetus, the bar for safety must be set extremely high.

The Surgeon General issued a specific advisory on cannabis use during pregnancy in 2019, citing concerns about the effects of THC on fetal brain development. The advisory emphasized that no amount of cannabis use during pregnancy or adolescence is known to be safe, and it urged healthcare providers to screen for cannabis use and counsel patients about the potential risks. The advisory also pointed out that today's cannabis products are much more potent than those of past decades.

It is important to understand why the consensus is so definitive despite the research being somewhat incomplete. Conducting randomized controlled trials of cannabis use in pregnant women is ethically impossible — you cannot intentionally expose fetuses to a potentially harmful substance to measure the effects. This means the evidence base relies primarily on observational studies, animal research, and epidemiological data, all of which have inherent limitations. However, when the available evidence consistently points toward potential harm — particularly to a population that cannot consent (the fetus) — medical ethics demands a conservative approach.

Some advocates argue that the medical establishment is overly cautious and that cannabis is being held to a stricter standard than other substances. While it is true that research limitations make definitive conclusions difficult, the biological plausibility of harm is well established. THC crosses the placental barrier, the fetal endocannabinoid system is active from early in development, and animal studies have demonstrated clear neurodevelopmental effects. Given these facts, the medical consensus is not merely political or cultural — it is rooted in biology.

How THC crosses the placental barrier

The placenta serves as the interface between mother and fetus, filtering nutrients and oxygen while ideally blocking harmful substances. However, the placenta is not an impenetrable shield, and THC passes through it with relative ease. THC is lipophilic (fat-soluble), so it readily crosses cell membranes, including the cell layers that make up the placental barrier. The CDC states that the chemicals in cannabis, THC in particular, pass through the mother's system to the baby.

What makes this particularly concerning is the timing of fetal brain development. The endocannabinoid system starts working early in pregnancy, and CB1 receptors are already present in the developing fetal brain. This system plays a crucial role in neural development, guiding the proliferation, migration, and differentiation of neurons. Endocannabinoids like anandamide act as signaling molecules that help determine where neurons go and how they connect. When exogenous THC enters this system, it has the potential to disrupt these precisely orchestrated developmental processes.

Animal studies have provided compelling evidence for this concern. Research in rodents has shown that prenatal THC exposure alters the expression of genes involved in neuronal development, disrupts the formation of dopaminergic and glutamatergic circuits, and produces lasting changes in the structure and function of the prefrontal cortex and hippocampus — brain regions critical for decision-making, attention, and memory. While animal models do not perfectly predict human outcomes, the consistency of these findings across multiple species and research groups is difficult to dismiss.

CBD's effects on fetal development are even less well understood than THC's; the CDC says they are currently unknown. In animal studies, high doses of CBD caused problems in the reproductive system of developing male fetuses. Because CBD modulates endocannabinoid signaling through indirect mechanisms — including inhibition of the FAAH enzyme that breaks down anandamide — it has the potential to alter endocannabinoid tone in the developing fetus even without directly activating cannabinoid receptors. The FDA "strongly advises against" using CBD, THC, or marijuana in any form during pregnancy or breastfeeding.

Research on fetal development and cannabis

The research on prenatal cannabis exposure and birth outcomes has grown considerably, with several large-scale studies providing useful data despite the methodological challenges inherent in observational research. The most consistently reported finding is an association between cannabis use during pregnancy and reduced birth weight. A 2016 meta-analysis in BMJ Open pooled 24 studies. It found that babies exposed to cannabis before birth were more likely to have low birth weight (below 2,500 grams), with pooled odds about 1.8 times higher, and weighed about 109 grams less on average.

However, the relationship between cannabis and birth outcomes is complicated by confounding factors. Women who use cannabis during pregnancy are more likely to also use tobacco, alcohol, or other substances, and they may differ from non-users in terms of socioeconomic status, nutrition, prenatal care access, and other variables that independently affect birth outcomes. Studies that carefully control for tobacco use — the most significant confounder — have found smaller but still statistically significant associations between cannabis use and reduced birth weight. A 2019 study in JAMA used Ontario birth registry data on 661,617 women. After matching cannabis users with similar non-users on tobacco use and other factors, it found that cannabis use was associated with a higher risk of preterm birth (relative risk 1.41).

The long-term neurodevelopmental effects of prenatal cannabis exposure have been examined in several prospective cohort studies, the most notable being the Ottawa Prenatal Prospective Study (OPPS) and the Maternal Health Practices and Child Development (MHPCD) study. These studies have followed children from birth into adolescence and adulthood, providing some of the best available longitudinal data. Both studies found subtle but measurable differences in executive function, attention, and impulse control among children with prenatal cannabis exposure, particularly those whose mothers used heavily during the first trimester. The MHPCD study also found associations with increased depressive symptoms and delinquent behavior in adolescence.

More recently, the Adolescent Brain Cognitive Development (ABCD) study — the largest long-term study of brain development in the United States — has begun to report findings on prenatal substance exposure. Preliminary analyses have shown that children with prenatal cannabis exposure exhibit differences in brain structure, including alterations in cortical thickness and white matter integrity. These differences were associated with increased psychopathology symptoms and lower cognitive test scores, though the effect sizes were generally small and the clinical significance remains debated.

It is also important to note what the research has not established: current evidence has not shown that prenatal cannabis exposure causes intellectual disability or major structural brain abnormalities, and evidence on specific birth defects is limited and inconsistent. The effects observed in research are subtle — they are statistical differences that emerge at the population level and may not be noticeable in any individual child. However, subtle does not mean insignificant. Small shifts in attention, impulse control, and executive function can have meaningful impacts on academic performance and social development over the course of a child's life.

Cannabis and breastfeeding

The transfer of cannabinoids into breast milk is well documented and presents a clear concern for nursing mothers. THC is highly lipophilic, and breast milk is one of the fattiest fluids the body produces, creating an efficient vehicle for cannabinoid delivery to the infant. A 2018 study published in Pediatrics tested 54 breast milk samples from 50 mothers who reported using cannabis. THC was detectable in 63% of them, up to about six days after last reported use. This long detection window reflects THC being stored in body fat and released slowly into breast milk.

The infant's exposure through breast milk is particularly concerning because of the immaturity of the newborn's metabolic systems. Adults process THC through a well-developed cytochrome P450 enzyme system in the liver, but this system is not fully functional in infants. This means that cannabinoids may accumulate to higher effective concentrations in the infant's body than they would in an adult's, and they may take longer to clear. The infant's blood-brain barrier is also more permeable than an adult's, potentially allowing greater cannabinoid access to the developing brain.

Despite these pharmacological concerns, the direct evidence of harm from cannabis exposure through breast milk is limited. No studies have definitively shown that the levels of THC typically found in breast milk cause measurable harm to infants. A small 1990 study found an association between maternal cannabis use during breastfeeding and slightly reduced motor development at one year of age, but the study was too small and too confounded to draw firm conclusions. More recent research has not yet filled this gap.

The American Academy of Pediatrics (AAP), ACOG, and the CDC all advise breastfeeding mothers to avoid cannabis completely. Breastfeeding has substantial, well-documented benefits. If you are breastfeeding and finding it hard to stop using cannabis, don't make the choice between the two on your own. Talk with your pediatrician, OB, or a lactation consultant, who can help you weigh the options for your situation without judgment.

Safer alternatives for pregnancy symptoms

Understanding why pregnant individuals turn to cannabis is essential for offering meaningful alternatives. The most commonly cited reason is nausea and vomiting. Morning sickness affects most pregnant women, and in its severe form (hyperemesis gravidarum), it can be debilitating and even life-threatening. Other symptoms that drive cannabis use include anxiety, insomnia, chronic pain, and appetite loss. Dismissing these symptoms or simply telling patients to "tough it out" is unlikely to change behavior; offering effective alternatives is far more productive.

For nausea and vomiting: Effective, pregnancy-tested options exist, from dietary changes and ginger to vitamin B6 and prescription anti-nausea medicines. The right choice and dose depend on how severe your symptoms are and on your medical history, so ask your OB or midwife about evidence-based options rather than self-treating. Severe vomiting (hyperemesis gravidarum) can cause dehydration and needs prompt medical care. Even when cannabis seems to ease nausea, there is no research showing it is safe to use for pregnancy nausea.

For anxiety: Talk-based therapies such as cognitive behavioral therapy (CBT), mindfulness programs designed for pregnancy, and regular moderate exercise like walking, swimming, or prenatal yoga can all help. If your anxiety is severe, your obstetrician and a mental health professional can discuss whether medication makes sense for you and which options have the best safety record in pregnancy.

For insomnia: Good sleep habits are the foundation of managing insomnia during pregnancy. Keep consistent sleep and wake times, limit screens before bed, keep the bedroom cool and dark, and avoid caffeine later in the day. A warm bath, relaxation techniques, and progressive muscle relaxation can also help. Don't start any sleep aid, including over-the-counter or "natural" products, without asking your OB or midwife first.

For chronic pain: Physical therapy, prenatal massage, warm compresses, and gentle stretching can help with musculoskeletal pain. Some common over-the-counter pain relievers are not recommended at certain stages of pregnancy, so ask your provider which pain relievers are appropriate for you and at what dose.

What to tell your healthcare provider

One of the most significant barriers to reducing cannabis use during pregnancy is the fear of judgment — or worse, legal consequences — that prevents many pregnant individuals from being honest with their healthcare providers. This fear is not unfounded: in some states, prenatal substance use can trigger involvement from child protective services, and urine drug testing during pregnancy is common, particularly in hospitals that serve lower-income populations. These policies, while intended to protect children, often have the unintended effect of driving cannabis use underground rather than eliminating it.

Despite these concerns, honesty with your healthcare provider is critically important. Your doctor or midwife needs to know what substances you are using in order to provide the safest possible prenatal care. Cannabis use can affect decisions about monitoring, testing, and treatment throughout pregnancy. Providers who are aware of cannabis use can offer appropriate support, discuss harm reduction strategies, and connect patients with resources to help them reduce or stop use. Most healthcare providers today are trained to approach substance use during pregnancy with empathy rather than judgment, and many are genuinely eager to help.

If you have been using cannabis during pregnancy, the most important thing to know is that stopping at any point is beneficial. The fetal brain continues developing throughout all three trimesters and into the postnatal period, so reducing exposure at any stage can reduce potential risk. Do not let guilt about past use prevent you from being honest going forward — your healthcare provider's goal is to support the healthiest possible outcome for you and your baby, not to punish you for past decisions.

If you are finding it difficult to stop using cannabis on your own, ask your provider about support resources. Many communities offer substance use counseling specifically designed for pregnant women, and these programs typically address cannabis alongside other substances in a non-judgmental environment. Some patients find that gradually reducing their dose — rather than stopping abruptly — is more sustainable and avoids the rebound anxiety and insomnia that can accompany sudden cessation. Your provider can help you develop a tapering plan if needed.

Finally, if you used cannabis before knowing you were pregnant — which is extremely common, as many pregnancies are unplanned and cannabis use in early pregnancy often predates pregnancy awareness — try not to catastrophize. The research on prenatal cannabis exposure describes statistical associations and subtle effects, not guaranteed outcomes. Many children with prenatal cannabis exposure develop normally and show no measurable differences from their peers. The best course of action is always to stop use as soon as pregnancy is confirmed and to work with your healthcare team to address the symptoms that were driving your cannabis use through safer alternatives.

Sources

1. Centers for Disease Control and Prevention. "Cannabis and Pregnancy." CDC, 2025. cdc.gov
2. U.S. Food and Drug Administration. "What You Should Know About Using Cannabis, Including CBD, When Pregnant or Breastfeeding." FDA Consumer Update. fda.gov
3. U.S. Food and Drug Administration. "FDA Regulation of Cannabis and Cannabis-Derived Products, Including Cannabidiol (CBD)." FDA. fda.gov
4. National Institute on Drug Abuse. "Substance Use While Pregnant and Breastfeeding." Substance Use in Women Research Report, NIDA. nida.nih.gov
5. Corsi DJ, et al. "Association Between Self-reported Prenatal Cannabis Use and Maternal, Perinatal, and Neonatal Outcomes." JAMA, 2019;322(2):145–152. PMC6582262
6. Bertrand KA, et al. "Marijuana Use by Breastfeeding Mothers and Cannabinoid Concentrations in Breast Milk." Pediatrics, 2018;142(3):e20181076. PMC6317767
7. Gunn JK, et al. "Prenatal exposure to cannabis and maternal and child health outcomes: a systematic review and meta-analysis." BMJ Open, 2016;6(4):e009986. PMID 27048634.