Cannabis chemicals cross the placenta, so a fetus can be exposed whenever a pregnant person uses marijuana. Research ties that exposure to lower birth weight, preterm birth, and subtle changes in attention and memory during childhood. The American College of Obstetricians and Gynecologists and the CDC both advise against cannabis use during pregnancy.
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How does cannabis reach a fetus?
THC, the main psychoactive compound in cannabis, passes through the placenta and enters fetal blood. It also reaches fetal brain tissue, where it binds to cannabinoid receptors that help guide brain development.
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CBD crosses the placenta as well. Animal studies show fetal THC levels can be lower than maternal levels, but the drug stays in fetal tissue long enough to affect developing systems. The body breaks THC down slowly, so repeated use builds up ongoing exposure.
What are the known risks during pregnancy?
- Lower birth weight and smaller head circumference
- Preterm birth, before 37 weeks
- Higher chance of stillbirth
- More NICU admissions after delivery
- Lower Apgar scores at birth
CDC tracking in several states shows infants exposed to cannabis in the womb are more likely to be born early and small. Those outcomes matter because low birth weight raises the risk of feeding problems, breathing issues, and jaundice in the first weeks of life.
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What about long-term effects on the child?
Studies of older children point to small differences in attention, memory, impulse control, and problem-solving. A widely cited review found that children exposed before birth scored lower on tests of attention and visual reasoning, though the gaps were modest. The evidence stays mixed because research methods vary and other factors, such as tobacco smoke and home environment, are hard to separate out.
Do the effects depend on how cannabis is used?
Smoking or vaping cannabis adds carbon monoxide and combustion byproducts that cut oxygen flow to the fetus. Edibles and concentrates can deliver large THC doses that stay in the body for hours longer. No delivery method has been shown to be safe during pregnancy.
Is CBD safe during pregnancy?
There is not enough research to call CBD safe in pregnancy. CBD can slow the liver's breakdown of THC and of some prescription drugs, which raises blood levels of both. Products sold as CBD also vary in purity, and some contain THC at levels the label does not mention.
Can cannabis treat morning sickness?
Some pregnant people use cannabis for nausea, but ACOG does not recommend it. Safer options exist, including vitamin B6, doxylamine, and prescription antiemetics. Talk to an obstetrician before trying anything for nausea, including herbal or over-the-counter products.
Does cannabis pass into breast milk?
THC shows up in breast milk and can reach a nursing infant. The American Academy of Pediatrics advises against cannabis use while breastfeeding. Because the data is thin, doctors cannot say how much exposure is safe, so most recommend avoiding it until more is known.
Why is the research on cannabis and pregnancy hard to read?
Most studies rely on self-reported use, and people tend to underreport drug use during pregnancy. Cannabis users also differ in tobacco, alcohol, and socioeconomic factors, and those factors carry their own risks for a baby. That makes it hard to pin every outcome on cannabis alone.
The pattern across studies points one direction: cannabis exposure in the womb is linked to worse birth outcomes. Confounders may inflate the numbers, but they do not erase the signal.
What should you do if you used cannabis before you knew you were pregnant?
Stop using it now and tell your doctor or midwife. One exposure early on does not mean harm is certain. Honest reporting helps your care team watch for issues and plan the right prenatal tests.
Quick answers to common questions
Can a fetus get high from cannabis?
THC reaches the fetal brain and binds to cannabinoid receptors, so exposure has direct effects on developing neural pathways. It is not a "high" in the adult sense, but the drug is active in fetal tissue.
How long does THC stay in a fetus?
THC and its metabolites can stay in the body for days to weeks. Repeated use keeps levels present, so exposure is ongoing rather than a single event.
Is there a safe amount of cannabis in pregnancy?
No threshold has been identified. Public health agencies advise stopping before conception and during pregnancy, and they treat any amount as a risk.
Does cannabis affect male fertility?
Yes, cannabis can lower sperm count and change sperm shape and movement. That matters for couples trying to conceive, since sperm health affects the odds of pregnancy.
Will a newborn be tested for cannabis?
Some hospitals screen meconium or umbilical cord tissue when there is a known exposure. A positive result may trigger a social work consult depending on state rules.
What this means for you
The clear takeaway is that no amount of cannabis is considered safe in pregnancy. If you are trying to conceive or already pregnant, stopping use is the step doctors recommend first. If you need help with nausea, sleep, or anxiety, ask your care team about options that have safety data behind them.
Legal cannabis is easy to buy in many states, but legal does not mean risk-free for a developing baby. Talk to a clinician if you have questions about your own use.