Stress, Hormones, and Eating

The investigators will develop a measure of endogenous opioid tone that might serve as a biological marker for drive for palatable food. Using a 'naltrexone probe,' the investigators will assess whether individual response to one dose of an opioid receptor antagonist, naltrexone, is related to non-homeostatic eating in non-pregnant women. Hypothesis 1: Naltrexone Response will be related to non-homeostatic eating. Hypothesis 2: Response profiles to the 25 mg dose will be slightly less in magnitude than the 50 mg dose. However, responses will be similarly related to non-homeostatic eating measures. Hypothesis 3: Response to naltrexone will be highly stable within individuals across time, in the absence of an intervention.