Effects of delta 9-THC, the principal psychoactive component of marijuana, during pregnancy in the rhesus monkey.

The effect of delta 9-tetrahydrocannabinol (THC), the principal psychoactive component in marijuana, was studied in pregnant and lactating rhesus monkeys. THC (2.5 mg/kg/d) or vehicle was administered during different periods of gestation, and effects on pregnancy outcome and hormone concentrations during pregnancy were studied. The most obvious effects were observed with administration early in pregnancy; three of five pregnancies aborted within days after the drug injections began, and one pregnancy resulted in a stillbirth at term. The three abortions were associated with a rapid decrease in chorionic gonadotropin and a subsequent fall in progesterone concentrations to nondetectable levels. In the two pregnancies that continued until term, estradiol concentrations were significantly higher than in vehicle control pregnancies. Daily THC administration during the middle or third portion of gestation resulted in lesser pregnancy loss (one premature birth and four live births at term with THC treatment during the middle portion; two premature births and three live births at term with THC treatment during the third portion). All the premature infants died within two weeks of birth. The weights of the infants at birth and weaning were not significantly different for the infants from vehicle control pregnancies and for full-term infants exposed to THC during gestation. Also, no effects on intrauterine growth and development were detected with ultrasound in the drug-treated pregnancies. With acute administration, THC readily crossed the placenta at term in rhesus monkeys and was transferred into the milk of nursing mothers. Significant blood levels of THC and depressant effects were observed in both mothers and neonates when the drug was administered to the mothers one hour before birth or during lactation.