Cannabis During Pregnancy: Current Research and Risks
A science-based overview of what is known — and what remains uncertain — about prenatal cannabis exposure, for patients, parents, and healthcare consumers.
- Definition: Prenatal cannabis exposure occurs when a pregnant person uses cannabis in any form — smoked, vaped, edible, or topical — and THC or other cannabinoids cross the placenta to reach the developing fetus.
- Prevalence: Rates of cannabis use during pregnancy have roughly doubled over the past decade as legalization has expanded and social stigma has declined.
- Why it matters: The fetal endocannabinoid system plays a critical role in brain development; external cannabinoids can disrupt this process at precisely the wrong time.
- Common misconception: Many people assume that because cannabis is "natural" or legally sold, it is safe during pregnancy — no medical authority supports this view.
- Medical consensus: The CDC, ACOG, AAP, and FDA all advise against any cannabis use during pregnancy and while breastfeeding.
- Research limitations: Most studies are observational and self-reported, making it difficult to isolate cannabis effects from confounding social and health factors.
What Is "Cannabis Use During Pregnancy"?
The phrase "cannabis use during pregnancy" — sometimes shortened in research literature to "prenatal cannabis exposure" or PCE — describes any consumption of cannabis products by a pregnant individual from conception through delivery. This includes smoking dried flower, vaping concentrates, consuming edibles or tinctures, applying topicals, and using CBD-only products. Because THC (delta-9-tetrahydrocannabinol) and other cannabinoids are lipid-soluble small molecules, they readily cross both the placental barrier and the fetal blood-brain barrier, meaning that whatever the mother consumes reaches the developing baby within minutes to hours of use.
Interest in this topic has surged over the past decade for two related reasons. First, cannabis legalization across many US states has normalized the plant and reduced perceived risk among the general population. Second, some pregnant individuals seek cannabis as a remedy for hyperemesis gravidarum — the severe nausea and vomiting of early pregnancy — because few conventional treatments provide complete relief. This combination of increased availability and a perceived medical rationale has contributed to a dramatic rise in prenatal use rates even as scientific concern has grown.
Historically, cannabis use during pregnancy was common in many cultures before the plant was criminalized in the early 20th century. The modern scientific study of its risks began in earnest only in the 1980s and accelerated after 2000 as longitudinal cohort studies began to follow children born to cannabis-using mothers into school age and adolescence. Those studies — including the landmark Ottawa Prenatal Prospective Study (OPPS) and the Adolescent Brain Cognitive Development (ABCD) study — have provided the most detailed data we currently have, though researchers acknowledge that isolating the effects of cannabis from poverty, stress, co-occurring substance use, and other variables remains a significant methodological challenge.
It is also important to note that cannabis laws vary by state. In states where cannabis is legal for adult recreational use, dispensaries are not always required to display pregnancy-specific warnings, and budtenders — while often knowledgeable about cannabis strains and consumer effects — are not medical professionals and should not be a primary source of prenatal health guidance. Always consult a licensed OB-GYN or midwife.
How Cannabis Affects the Developing Fetus
To understand why cannabis poses risks during pregnancy, you first need to understand the endocannabinoid system (ECS). The ECS is a network of receptors — primarily CB1 and CB2 — along with the body's own naturally produced cannabinoids (called endocannabinoids, such as anandamide and 2-AG) that regulate a vast array of physiological processes: mood, appetite, pain, memory, immune function, and, critically, fetal brain development. You can learn more in our explainers library on the endocannabinoid system.
Think of the ECS during fetal development like a set of traffic lights guiding neurons to their correct destinations in the growing brain. Endocannabinoids act as precise, locally produced signals that tell neurons when to migrate, when to connect, and when to prune unnecessary connections. When THC from cannabis enters the fetal brain, it essentially hijacks those traffic lights — binding to CB1 receptors far more powerfully and for far longer than the body's own endocannabinoids do. The result is a disruption of the timed signaling that orchestrates normal neural architecture.
The CB1 receptor is expressed in fetal brain tissue as early as the first trimester, meaning there is no truly "safe" window of pregnancy during which THC exposure is without neurological risk. By the third trimester, the fetal hippocampus — a brain region central to memory, learning, and emotional regulation — is especially vulnerable because it undergoes rapid growth and synaptic formation during this period.
Beyond neurodevelopment, THC also affects placental function. Research has shown that THC can impair placental blood flow and oxygen delivery by interacting with CB1 receptors in placental tissue, which may help explain the association between prenatal cannabis use and low birth weight. Studies of cannabis effects on the adult cardiovascular system provide a parallel: just as THC can cause acute changes in heart rate and blood pressure in adults, it can alter vascular tone in the placenta with downstream consequences for fetal growth.
"The fetal brain is essentially under construction during the entire pregnancy, and the endocannabinoid system is part of the scaffolding. Introducing exogenous THC is like removing bolts from that scaffolding mid-build." — Paraphrased from research presented at the Society for Neuroscience annual meeting
Key Data & Research
The evidence base on prenatal cannabis exposure has grown substantially since 2010. Below is a summary of findings from major studies and surveillance data. While individual studies vary in methodology and population, the overall direction of evidence points consistently toward harm.
| Outcome Studied | Key Finding | Source / Study | Strength of Evidence |
|---|---|---|---|
| Stillbirth | 2–4× increased odds among cannabis users | Varner et al., AJOG, 2014 | Moderate (large cohort, but self-report) |
| Low birth weight (<2,500g) | ~50% higher likelihood with prenatal use | Gunn et al., BMJ Open, 2016 meta-analysis | Moderate-strong (meta-analysis of 24 studies) |
| Preterm birth (<37 weeks) | 1.4–1.9× increased risk | Conner et al., Obstetrics & Gynecology, 2016 | Moderate |
| Child attention & executive function | Deficits in attention, impulse control at ages 6–12 | Ottawa Prenatal Prospective Study (OPPS) | Strong (longitudinal, 40+ years) |
| Child anxiety & depression | Elevated internalizing symptoms at ages 9–10 | ABCD Study, JAMA Psychiatry, 2020 | Strong (11,000+ participants) |
| Substance use disorder risk | Higher odds of SUD in exposed adolescents | Paul et al., Drug & Alcohol Dependence, 2021 | Moderate |
| THC in breast milk | Detectable for up to 6 days after a single use | Bertrand et al., Pediatrics, 2018 | Moderate |
It is worth noting that modern cannabis products are dramatically more potent than those studied in early research. The average THC concentration in retail cannabis has increased from roughly 4% in the 1990s to over 12–15% in flower and 60–90% in concentrates. This means that risk estimates from older studies may actually underestimate current risks. Our explainers on THC potency explore this trend in more detail.
| Position / Organization | Official Recommendation on Cannabis in Pregnancy | Notes |
|---|---|---|
| CDC (Centers for Disease Control) | Do not use cannabis during pregnancy or breastfeeding | Includes all forms: smoked, edible, CBD |
| ACOG (American College of OB-GYNs) | Advises against use; screen and counsel all patients | Committee Opinion #722, updated 2023 |
| AAP (American Academy of Pediatrics) | No safe level of use in pregnancy or while nursing | Urges pediatricians to counsel parents proactively |
| FDA | Strongly advises against CBD, THC, or CBN products | Specifically calls out CBD marketed as supplements |
| SAMHSA | Recommends cessation; provides treatment referrals | National helpline: 1-800-662-4357 |
Practical Implications for Cannabis Consumers
For the millions of Americans who are regular cannabis consumers and are pregnant, trying to conceive, or breastfeeding, the research landscape has direct practical implications. Here is what current evidence and medical consensus suggest:
If you are trying to conceive: Both male and female fertility can be affected by regular cannabis use. THC has been linked to reduced sperm motility and alterations in sperm DNA methylation in males, and to disrupted ovulatory cycles in females. While the data here is less definitive than for pregnancy itself, the prudent approach recommended by most reproductive endocrinologists is to cease cannabis use when actively trying to conceive. Explore our medical cannabis section for research on cannabis and fertility.
If you are currently pregnant: Stop all cannabis use immediately and inform your OB-GYN or midwife of prior use without fear of judgment. Most healthcare providers are trained to have these conversations supportively. If you were using cannabis to manage nausea, ask your provider about evidence-based alternatives such as vitamin B6, doxylamine, or in severe cases, prescription antiemetics. Stopping cannabis use at any point in the pregnancy reduces the total dose of THC reaching the fetus and is always beneficial compared to continued use.
If you are breastfeeding: THC concentrates in breast milk at levels up to eight times higher than in maternal plasma due to the fat-soluble nature of cannabinoids. It remains detectable in breast milk for up to six days after a single use. The AAP advises that parents who use cannabis should not breastfeed. Formula feeding is a safe alternative that eliminates this exposure pathway entirely.
For dispensary staff and industry workers: In states where cannabis is legal, there is a growing responsibility for point-of-sale education. Several states now mandate pregnancy warning labels on cannabis packaging. Staff should be prepared to respectfully direct any pregnant or potentially pregnant customer to consult their healthcare provider and should never make medical claims about cannabis safety during pregnancy. Responsible messaging matters — particularly as younger…