Cannabis and Pregnancy: What Research Shows About Risks in 2026

As cannabis legalization expands across the United States, an uncomfortable but critical question demands clear, evidence-based answers: what does the science actually say about cannabis use during pregnancy? With more women of childbearing age reporting cannabis use than at any point in recorded history, and with morning sickness remaining one of the most commonly cited reasons for use during pregnancy, the stakes of getting this conversation right could not be higher.

The research landscape has grown substantially since 2020, and the picture it paints is increasingly detailed — though not yet complete. Here is what we know, what remains uncertain, and what medical experts are telling their patients in 2026.

The Prevalence Question

Before diving into outcomes, the scope of the issue matters. Data from the National Survey on Drug Use and Health indicates that approximately 7-8% of pregnant women in the United States report using cannabis at some point during pregnancy, with rates highest during the first trimester. In states with legal recreational markets, self-reported use rates are even higher, reaching 10-12% in some surveys.

These numbers almost certainly undercount actual use. Stigma around substance use during pregnancy creates strong incentives for underreporting, and urine screening studies have consistently found higher rates of THC metabolites than self-reports would predict. A reasonable estimate is that somewhere between 8-15% of pregnancies in legal states involve some cannabis exposure.

The primary driver of use is nausea and vomiting. Hyperemesis gravidarum — severe pregnancy-related nausea — affects roughly 2% of pregnancies and can be debilitating. For women experiencing persistent nausea that does not respond well to conventional treatments, the temptation to try cannabis is understandable, particularly when they see it marketed as a natural remedy in dispensaries.

What the Research Shows

Fetal Growth and Birth Weight

The most consistent finding across multiple studies is an association between regular cannabis use during pregnancy and reduced birth weight. A 2024 meta-analysis published in JAMA Pediatrics, pooling data from 42 studies and over 130,000 pregnancies, found that regular cannabis use (defined as weekly or more frequent) was associated with an average reduction in birth weight of approximately 100-150 grams and a modestly increased risk of being classified as small for gestational age.

This effect size is comparable to tobacco smoking during pregnancy, though separating the two exposures is methodologically challenging since many cannabis users also smoke tobacco. Studies that have attempted to isolate cannabis-only exposure still find a birth weight effect, but the magnitude is somewhat smaller.

Preterm Birth

Evidence on preterm delivery is more mixed. Several large cohort studies have found a modest association between cannabis use and preterm birth, with adjusted odds ratios typically ranging from 1.2 to 1.5. However, confounding variables — including socioeconomic factors, stress, and concurrent use of other substances — make it difficult to establish a clear causal relationship. The most carefully controlled studies tend to find weaker associations, suggesting that at least some of the observed effect may be attributable to confounders rather than cannabis itself.

Neurodevelopmental Outcomes

This is where the science gets both most concerning and most uncertain. The endocannabinoid system plays a critical role in fetal brain development, regulating neuronal proliferation, migration, and synapse formation. THC crosses the placental barrier readily and can interact with this system during critical developmental windows.

Several longitudinal studies have tracked children with prenatal cannabis exposure. The Ottawa Prenatal Prospective Study and the Maternal Health Practices and Child Development Study, both initiated decades ago, have provided some of the longest follow-up data. These studies have reported subtle but measurable differences in executive function, attention, and impulse control in exposed children, with effects becoming more apparent in school-age years rather than infancy.

More recent studies using advanced neuroimaging have identified structural differences in brain regions involved in executive function among children with heavy prenatal cannabis exposure. A 2025 study in Biological Psychiatry using data from the ABCD (Adolescent Brain Cognitive Development) study found altered cortical thickness patterns in children whose mothers reported regular cannabis use during pregnancy.

The critical caveat is that these effects are subtle and overlapping with many other influences on child development. No study has identified a catastrophic neurodevelopmental outcome specifically attributable to prenatal cannabis exposure, and the effect sizes are generally smaller than those associated with prenatal alcohol exposure. But subtle does not mean insignificant, particularly when aggregated across a population.

Placental Function

Emerging research has examined how cannabinoids affect placental biology. The placenta expresses cannabinoid receptors, and in vitro studies have shown that THC can alter placental cell function, including nutrient transport and immune signaling. A 2025 study from the University of Western Ontario found that THC exposure altered the expression of genes involved in placental vascularization, potentially explaining some of the observed effects on fetal growth.

The Route of Administration Problem

One underappreciated aspect of this discussion is that most historical research involves smoked cannabis. Combustion products introduce carbon monoxide and other toxins that independently affect fetal development. As more consumers shift to edibles, vaporizers, and other non-combustion methods, the question of whether route of administration matters becomes increasingly relevant.

Limited research suggests that the THC-specific effects — those mediated through the endocannabinoid system — would persist regardless of delivery method, but the combustion-related effects would be eliminated. This means that switching from smoking to edibles might reduce some risks but would not eliminate concerns related to THC itself crossing the placental barrier.

What Medical Organizations Recommend

The consensus among major medical organizations remains unequivocal. The American College of Obstetricians and Gynecologists, the American Academy of Pediatrics, and the Society for Maternal-Fetal Medicine all recommend against cannabis use during pregnancy and breastfeeding. Their position is based on the precautionary principle: given evidence of potential harm and no established safe threshold, avoidance is the recommended approach.

This recommendation extends to CBD products. While CBD does not produce intoxication, it does interact with the endocannabinoid system, and its effects on fetal development are even less studied than those of THC. Additionally, many CBD products contain trace amounts of THC, and the supplement market remains inconsistently regulated in terms of label accuracy.

The Breastfeeding Question

THC is lipophilic and accumulates in breast milk at concentrations roughly 2-8 times higher than maternal plasma levels. Studies have detected THC metabolites in infant urine following breastfeeding by cannabis-using mothers, confirming that the infant is exposed. The effects of this exposure on infant development remain poorly characterized, but given what we know about the importance of the endocannabinoid system in early brain development, most experts recommend against cannabis use while breastfeeding.

A Nuanced Reality

The science on cannabis and pregnancy does not support panic, but it does support caution. The effects identified in research are generally subtle rather than dramatic, and many women who used cannabis during pregnancy before it was widely discouraged have healthy children. But population-level research consistently identifies measurable differences in outcomes, particularly with regular use.

For women experiencing severe nausea during pregnancy, the conversation should be with their healthcare provider about FDA-approved anti-nausea medications and evidence-based alternatives — not with a budtender at a dispensary. The stakes are simply too high, and the evidence too consistent in its direction, to treat cannabis as a benign option during this critical developmental window.

As research continues, we may develop a more granular understanding of dose-response relationships, critical exposure windows, and individual risk factors. Until then, the precautionary approach remains the scientifically responsible one.