Effects of chronic methadone treatment on maternal body weight and food and water consumption in rats.

Body weight gain and food and water consumption of female rats receiving daily methadone injections (5 mg/kg) intraperitoneally prior to mating and during gestation and lactation were studied. In contrast to saline-injected mothers, methadone-treated females had lower body weights throughout pregnancy, but gained weight during lactation; by postnatal day 21, both groups were of comparable body weight. No significant differences in food consumption throughout gestation or lactation were recorded. Total water consumption of methadone-treated rats was higher during the first 2 weeks of gestation and lactation, and lower during the 3rd week of lactation when compared to controls. These results demonstrate that methadone-treated rats have lower body weights throughout gestation and lactation, and that these weight deficits are not caused by insufficient food and water consumption.