Morphine and brain growth retardation in the rat.

Fetal and infant rats were maternally exposed to morphine sulfate during gestation and lactation. Drug was administered twice daily by i.p. injection, with dosages gradually increased from 10 mg/kg/injection to a maintenance level of 40 mg/kg/injection. Offspring during the preweaning period had a reduction in body, brain and cerebellar weights, as well as in brain length and cerebral and cerebellar widths. Deficits persisted in young rats observed 51/2 weeks after cessation of drug exposure and in animals continuing to receive twice daily i.p. injections of 20 mg/kg/injection. These results indicate that maternal morphine treatment retards the growth of young rats and impairs brain development.