A series of (3R*,4R*)-3,4-dimethyl-4-(3-hydroxyphenyl)piperidine opioid antagonists with varying substituents on the nitrogen were evaluated for their effect on food consumption in obese Zucker rats. Opioid affinity (mu, kappa, and delta for selected compounds) and opioid antagonist activity (mu and kappa) were characterized and compared to effects on food consumption. No compounds with high selectivity for either mu or kappa receptors were discovered. However, compounds in the series had exceptional potency as opioid antagonists and in reducing food consumption in the obese Zucker rat. In contrast, a few compounds with high potency as opioid antagonists had much weaker potency for inhibiting food consumption. (3R,4R)-3,4-Dimethyl-1-[(3S)-3- hydroxy-3-cyclohexyl-propyl]-4-(3-hydroxyphenyl)piperidine (11,LY255582) emerged as having the best activity profile, both in reducing food consumption and as an opioid antagonist. Compound 11 is a highly potent mu, kappa-, and delta-opioid antagonist with possible clinical utility as an appetite suppressant for weight loss.