Critical periods for marihuana-induced intrauterine growth retardation in the rat.

Pregnant rats were intubated with marihuana extract (20, 200 mg/kg) throughout gestation. Control animals were intubated with vehicle (olive oil). Control animals and animals treated with the lower dose of drug were pair-fed and pair-watered to animals treated with the high dose. At parturition, pups were counted, weighed, culled, and assigned to nondrug-treated dams. Marihuana reduced food and water consumption and maternal weight gain. Pup weight at birth was reduced and neonatal mortality was increased in offspring exposed during the third week of gestation or throughout gestation. Litter size, postnatal mortality and weight at weaning were not significantly affected.