Reproductive Health
Fertility, pregnancy, fetal development, and the evidence base
The endocannabinoid system plays a critical role in reproductive biology — from ovulation and implantation to fetal brain development and lactation. Cannabis use during pregnancy is rising, driven partly by use for nausea and anxiety, yet the evidence on fetal and neonatal outcomes raises significant safety concerns.
What the Research Shows
Endocannabinoid signaling is essential throughout reproduction. Anandamide and 2-AG regulate ovarian function, uterine receptivity, embryo implantation, and placental development. CB1 receptors are expressed in sperm, oocytes, and the developing fetal brain from early gestation. THC crosses the placenta and blood-brain barrier, and is detectable in breast milk for up to 6 days after use. The most consistent clinical finding is that prenatal cannabis exposure is associated with adverse neurodevelopmental outcomes in offspring — including lower birth weight, increased preterm birth risk, and later cognitive, behavioral, and psychiatric problems. These associations persist after controlling for tobacco use and socioeconomic factors in most large cohort studies. For fertility, THC appears to impair sperm motility and function, and may disrupt ovulation and implantation. Despite these concerns, cannabis use in pregnancy has increased substantially — a 2023 US survey found 7% of pregnant women reported past-month use, with many citing morning sickness as the primary reason. No safe level of cannabis use in pregnancy has been established.
Key Findings
Prenatal cannabis exposure is associated with lower birth weight
Well-StudiedMeta-analyses of 24+ cohort studies find prenatal cannabis exposure associated with ~109g lower birth weight and increased odds of low birth weight (<2500g), independent of tobacco use.
THC impairs sperm motility and function
Emerging ResearchMultiple studies show THC reduces sperm motility, alters morphology, and impairs the acrosome reaction. Effects appear dose-dependent and partially reversible with cessation.
Prenatal exposure linked to neurodevelopmental problems in offspring
Emerging ResearchLongitudinal cohort studies (ABCD, ALSPAC, Generation R) find associations between prenatal cannabis exposure and increased ADHD symptoms, anxiety, depression, and lower cognitive scores in children aged 6–14.
THC is detectable in breast milk for up to 6 days
Well-StudiedPharmacokinetic studies confirm THC transfers into breast milk at concentrations that could expose nursing infants to psychoactive doses, particularly with frequent use.
Featured Studies
View all in libraryCommon Questions
What We Still Don't Know
These are open research questions — areas where the evidence is insufficient or actively contested.
- 1Is there a safe window or dose of cannabis use in pregnancy that does not affect fetal outcomes?
- 2What are the long-term psychiatric outcomes (beyond age 14) of prenatal cannabis exposure?
- 3Does CBD (without THC) carry the same reproductive risks as THC?
- 4How does cannabis affect IVF success rates and embryo quality?
- 5What is the mechanism linking prenatal cannabis exposure to ADHD and anxiety in offspring?
- 6Does paternal cannabis use at conception affect offspring outcomes?