Major medical groups, including the American College of Obstetricians and Gynecologists (ACOG) and the Centers for Disease Control and Prevention (CDC), advise against cannabis use at any point in pregnancy or while breastfeeding. THC crosses the placenta and reaches the fetus, and studies link use during pregnancy to low birth weight, preterm birth, and differences in attention and behavior in children. No safe amount and no safe trimester has been identified.

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How does THC get from a pregnant person to the fetus?

Delta-9 THC is small and fat-soluble, which lets it cross the placental barrier into fetal blood. The fetal liver clears THC at a slower rate than an adult liver, so the compound can stay in the baby's system longer than it would in an adult. Cannabis smoke adds a second problem: carbon monoxide and tar from burned plant material cut oxygen flow to the fetus.

Cannabis Use During the Third Trimester of Pregnancy

Cannabis products sold today are stronger than the flower used in older studies. Vape oils and concentrates carry the highest THC levels, and dose accuracy on edibles is often poor.

can marijuana cause birth defects

What pregnancy risks are linked to cannabis?

Most evidence comes from observational studies, since researchers cannot assign pregnant people to use cannabis in a controlled trial. That limits how firmly any single outcome can be tied to cannabis alone, because alcohol, tobacco, and other factors often appear in the same group.

Doctors' Advice on Cannabis Use During Pregnancy

Even with that caveat, several patterns repeat across studies:

Surveys show that a share of pregnant people report cannabis use, with rates that shift by age group and by state. That means a prenatal provider may ask about use at the first visit and again later.

Why is the research on cannabis and pregnancy limited?

Researchers cannot run a randomized trial that exposes a fetus to a substance under study, so almost all data comes from people who chose to use or not use. Those two groups differ in income, tobacco use, mental health, and prenatal care, which makes causation hard to prove. Self-reporting is also imperfect, since some people underreport use out of concern about legal or child welfare consequences.

Does the form of cannabis matter?

Is smoking worse than edibles?

Smoking and vaping add carbon monoxide and airway irritants, so they carry risks that edibles do not. Edibles still deliver THC to the bloodstream and to the fetus, so switching forms does not remove the main concern. Doses in edibles vary from product to product, and testing has found labels that understate THC content.

Is CBD safe during pregnancy?

The FDA advises against CBD use during pregnancy and while breastfeeding. CBD sold online is not FDA-approved, and lab testing has found products that contain THC or more CBD than the label claims. The effect of CBD on a human fetus is not known, and animal studies at high doses showed harm to the reproductive system in male offspring.

Can cannabis treat morning sickness?

There is no evidence that cannabis treats nausea in pregnancy better than approved options, and the fetal risks outweigh any relief. ACOG points pregnant people toward treatments with a safety record, such as vitamin B6 plus doxylamine, ginger, and small meals eaten through the day. A clinician can add a prescription antiemetic when those steps fall short.

What about cannabis and breastfeeding?

THC passes into breast milk and can be detected in nursing infants. ACOG discourages cannabis use while breastfeeding, and the same advice applies to CBD. If you need help with sleep, pain, or anxiety after birth, ask your provider about options that have data behind them during lactation.

What should you do if you used cannabis before you knew you were pregnant?

  1. Stop using cannabis and CBD products now.
  2. Tell your prenatal provider. Screening is meant to guide care, not to judge.
  3. Keep every prenatal visit and follow the testing your provider recommends.
  4. Ask for help if you use other substances or find it hard to stop.

One practical note: in some US states, a positive drug screen at delivery can trigger a child welfare referral. Rules differ by state, so ask your provider what applies where you live.

Frequently asked questions

Does secondhand cannabis smoke affect a pregnancy?

Research on secondhand cannabis smoke and birth outcomes is thin. The safest step is to keep smoke out of the home and car, since secondhand tobacco smoke is a known risk in pregnancy.

How long does THC stay in a newborn?

THC and its metabolites can show up in meconium for months after exposure and in umbilical cord tissue at birth. A urine test on a newborn shows recent exposure only. Detection windows depend on the test used, not on how much harm occurred.

Is one trimester safer than another?

No trimester is considered safe. The fetal brain develops through all three trimesters, and THC exposure at any stage is a concern. Limited data on first-trimester use is not the same as proof of safety.

For anyone weighing cannabis for sleep, anxiety, or nausea during pregnancy, the guidance from every major medical body is the same: hold off and pick a safer option. A prenatal provider can help you find one.