Morphine selectively influences macronutrient intake in the rat.

Dietary self-selection of the three macronutrients, protein, carbohydrate and fat, was examined in male rats following the administration of three doses of morphine sulphate: 10 mg, 15 mg, and 30 mg/kg body weight. Intakes of all three macronutrients were suppressed in a dose-dependent manner for a two-hour period following morphine administration. Both protein and carbohydrate intakes remained suppressed for a six-hour feeding period after morphine injections. In contrast, animals increased fat intake during the final four hours of the six-hour feeding period resulting in an overall increase in fat intake.