Cannabis is the most commonly used illicit substance during pregnancy in the United States. Use has increased substantially over the past decade, accelerated by legalization, falling risk perception, and the widespread but unsupported belief that cannabis is a safe remedy for pregnancy nausea. An estimated 7–10% of pregnant women report cannabis use, with rates higher in younger age groups and in states with legal cannabis markets. Every major medical organization, including ACOG, AAP, ACMG, and the CDC, advises against cannabis use during pregnancy. The position is grounded in a substantial and growing body of data linking prenatal cannabis exposure to serious fetal, neonatal, and developmental harms.
Why Cannabis Reaches the Fetus
THC, the primary psychoactive compound in cannabis, readily crosses the placenta and enters the fetal bloodstream. It also accumulates in amniotic fluid and is detectable in breast milk, providing routes of fetal and infant exposure beyond direct placental transfer. Unlike many drugs, THC is highly lipophilic (fat-soluble); it concentrates in fatty tissues including the fetal brain.
The developing fetal brain is especially vulnerable to THC exposure for a specific neurobiological reason: the endocannabinoid system plays a critical regulatory role in fetal brain development throughout pregnancy. CB1 receptors are expressed in the developing embryonic brain as early as the first trimester and guide neuronal migration, synaptogenesis, and circuit formation. Exogenous THC that disrupts this signaling does not simply have the psychoactive effects it has in adults; it interferes with the developmental program that the endocannabinoid system is running in a rapidly constructing nervous system.
What Marijuana Use During Pregnancy Does to Birth Outcomes
Large studies, including one from 2024 that looked at nearly 8 million pregnancies, have found consistent links between marijuana use during pregnancy and serious complications at birth. Here is what the research shows in plain terms:
Why Pregnant Women Use Cannabis, and Why Nausea Is Not a Valid Reason
The most commonly reported reason for cannabis use during pregnancy is nausea and vomiting of pregnancy (NVP), commonly called morning sickness, which affects up to 80% of pregnant women and can be debilitating in severe cases. Many women who use cannabis for NVP describe genuine symptom relief. Dispensaries in legal states routinely recommend cannabis for pregnancy nausea. Social media perpetuates this recommendation widely.
The clinical consensus, based on the evidence reviewed above, is that cannabis use for pregnancy nausea is not supported by safety data and should not be recommended. No clinical trial evidence demonstrates that cannabis is safe for fetal development at any dose or trimester. The fetal risks documented in the evidence base do not become acceptable because the substance provides short-term nausea relief to the mother. The FDA has approved safe pharmacological alternatives for NVP, including doxylamine-B6 combinations and ondansetron for severe cases, that do not carry the same fetal risk profile.
ACOG, the American Academy of Pediatrics, and the CDC all explicitly advise pregnant and breastfeeding women to avoid cannabis entirely. The ACOG position statement notes that no amount of cannabis has been established as safe during pregnancy.
Neurodevelopmental Outcomes in Children
Beyond the immediate birth outcomes, prenatal cannabis exposure has been linked to a range of neurodevelopmental outcomes in children followed longitudinally. The endocannabinoid system’s role in fetal brain development makes this the most biologically plausible pathway for long-term harm, and the data, though more complex than the birth outcomes data, is concerning.
The ABCD (Adolescent Brain Cognitive Development) study, the largest longitudinal study of child brain development in the US, has been a primary data source for prenatal cannabis outcomes. Associations documented in children with prenatal cannabis exposure include:
The Sorkhou et al. 2024 meta-analysis synthesized behavioral and cognitive outcomes in young children (infancy through early childhood) and found that while low birthweight, preterm birth, and NICU admission were robustly confirmed, the evidence for behavioral and cognitive harms at early ages was more variable. However, the authors noted associations with poorer attention and externalizing problems as the most consistently emerging findings. The neurodevelopmental signal is real; the full magnitude and spectrum of longer-term outcomes is still being established as cohorts age.
Neonatal Withdrawal
Neonates born to women who used cannabis regularly during pregnancy may show signs of neonatal withdrawal syndrome, sometimes called neonatal abstinence syndrome (NAS) in this context. Findings in cannabis-exposed newborns have included increased jitteriness, prolonged high-pitched crying, abnormal startles, and feeding difficulties in the first days after birth. These findings are less severe than opioid-associated NAS but represent a detectable physiological response to THC withdrawal in the neonate whose endocannabinoid system has been chronically stimulated during gestation.
The Role of Potency and Timing
Two important moderators of risk deserve clinical attention. First, cannabis potency has increased dramatically. The THC concentrations available today (15–30% in flower, up to 80% in concentrates) are far higher than those in studies conducted even a decade ago. Dose-response relationships for fetal harm have not been fully characterized, but the biological mechanisms are dose-dependent; higher THC exposure to the fetus produces greater endocannabinoid system disruption.
Second, timing matters. First-trimester exposure occurs during the period of rapid fetal organogenesis, when structural anomalies and major organ development are at stake. Second and third-trimester exposure involves a developing but structurally assembled brain and fetus, with ongoing synaptogenesis and circuit maturation as the primary targets. All trimesters carry risk through different mechanisms, and there is no established “safe window” for cannabis use during pregnancy.
Professional Perspective
Research on marijuana use during pregnancy has grown significantly in recent years. We now have multiple large studies, some covering millions of pregnancies, that paint a consistent picture of risk. One of the most rigorous was a 2024 systematic review that specifically focused on women who used cannabis but not tobacco, which allowed researchers to isolate marijuana’s effects rather than having the results clouded by smoking. The findings were clear and concerning.
“Prenatal cannabis exposure is associated with stillbirth, intrauterine growth restriction, and impaired fetal neurodevelopment.”
What This Means When Looking for Treatment
For pregnant women seeking help with cannabis use disorder, or for anyone supporting a pregnant person who uses cannabis, the evidence is clear that cessation is the most important step for fetal health. There is no established safe dose or safe window for cannabis during pregnancy. Pregnancy is one of the highest-motivation periods for cessation, and treatment programs experienced in perinatal substance use disorders are available and effective. Addressing cannabis use during pregnancy is the most direct available intervention to reduce documented harm to the developing baby.