The question of whether using cannabis during pregnancy poses a risk is increasingly relevant as legalization expands. Current scientific and medical consensus strongly advises against cannabis use at any point during pregnancy or while breastfeeding. This recommendation applies to all forms, including smoked, vaporized, edible, or topical preparations, as the active chemical compounds readily enter the body’s systems. The primary concern centers on the psychoactive compound delta-9-tetrahydrocannabinol (THC) and, to a lesser extent, cannabidiol (CBD), both of which can directly affect the developing fetus.
How Cannabis Compounds Reach the Fetus
The placenta is not an impenetrable barrier to cannabis compounds. THC is highly fat-soluble, meaning it easily passes through lipid-rich membranes, including the placental barrier, and enters the fetal circulation. Studies confirm that THC concentrations in the fetal bloodstream can be significant, though typically lower than the mother’s serum concentration.
Once in the fetal system, THC and other cannabinoids interact with the naturally occurring endocannabinoid system (ECS). The ECS is a complex signaling network present from the earliest stages of embryonic development, playing a role in implantation, cell migration, and the formation of neural circuits. This system involves receptors like CB1 and CB2, which are abundant in the developing brain and placenta.
Introducing external cannabinoids like THC disrupts the precise signaling of the natural ECS. This interference during rapid fetal development can alter the trajectory of neurogenesis (forming new neurons) and synaptogenesis (forming connections between neurons). The ECS also plays a functional role in the placenta, and its disruption by external cannabinoids may negatively affect placental health.
Impact on Fetal Growth and Birth Outcomes
Prenatal cannabis exposure is associated with measurable physical consequences observed at birth. One consistently reported finding is an increased risk for restricted fetal growth. Infants exposed to cannabis in utero are more likely to have a lower birth weight, often averaging 100 to 150 grams less than unexposed infants, even after accounting for other factors like tobacco use.
This growth restriction can result in the infant being classified as small for gestational age (SGA). Exposed infants may also have a smaller head circumference, which suggests altered brain development. These physical growth deficits appear most pronounced with continued cannabis use throughout pregnancy.
Cannabis exposure is linked to an increased risk of preterm birth (delivery before 37 weeks of gestation). Preterm birth can lead to complications for the newborn, including respiratory distress and difficulty maintaining body temperature. Consequently, infants exposed to cannabis in utero have a higher likelihood of requiring admission to the neonatal intensive care unit (NICU).
Neurodevelopmental and Behavioral Effects in Childhood
The long-term consequences of prenatal cannabis exposure primarily involve subtle, enduring alterations in neurodevelopment. Since the ECS is deeply involved in wiring the fetal brain, external cannabinoid exposure may result in persistent changes to brain structure and function. These effects are often not immediately apparent at birth but become detectable as the child grows and complex cognitive demands increase.
One area of concern involves executive function, which encompasses higher-level cognitive skills like planning, problem-solving, and impulse control. Children with prenatal exposure have shown subtle difficulties with tasks requiring sustained attention and the ability to inhibit inappropriate responses. This includes an observed increase in attention deficits, sometimes manifesting as symptoms similar to Attention-Deficit/Hyperactivity Disorder (ADHD).
Memory issues, particularly those related to short-term or working memory, have been associated with exposure. These cognitive changes may affect academic achievement and overall learning capacity in childhood and adolescence. Researchers have found that these effects can be detected well into late childhood and early adulthood, suggesting they represent lasting changes rather than temporary delays.
In terms of behavior, evidence links prenatal cannabis exposure to an increased risk of externalizing behaviors, such as delinquency and aggression, during adolescence. Some studies suggest a greater susceptibility to mental health issues later in life, including increased risk of depressive illness and symptoms related to psychosis. These neurodevelopmental findings highlight the brain’s vulnerability to cannabinoid interference during its rapid growth phases.
Official Medical Guidance and Cessation Resources
Major medical organizations, including the American College of Obstetricians and Gynecologists (ACOG), strongly recommend complete abstinence from cannabis use during prepregnancy, pregnancy, and lactation. This guidance is based on accumulating evidence of adverse fetal and developmental outcomes and the fact that THC transfers into breast milk. There are currently no medical indications for cannabis use during pregnancy supported by scientific data.
A common misconception is that cannabis can safely treat pregnancy-related symptoms like nausea or vomiting. Healthcare providers are advised to counsel patients about alternative, non-cannabis options that have established safety profiles for managing these symptoms. The recommendation to abstain is universal because no safe threshold of use has been established for the developing fetus.
Healthcare professionals are encouraged to screen all pregnant patients for cannabis use in a nonjudgmental manner. If a patient is using cannabis, the focus shifts to non-punitive, supportive strategies to encourage cessation. Patients should speak openly with their providers to access resources, such as substance use support programs, which offer motivational interviewing and behavioral change strategies.
While continued cannabis use is strongly discouraged during lactation, the known health benefits of breastfeeding generally outweigh the risks of low-level THC transfer. Cessation efforts should be prioritized over discouraging breastfeeding altogether. The primary goal is to support the patient in achieving complete abstinence to protect the health of the child.