Effect of phenylpropanolamine on energy expenditure and weight loss in overweight women

The effect of phenylpropanolamine (PPA), a noncatecholamine sympathomimetic weight-loss agent, on energy expenditure (EE) and substrate oxidation was measured in a respiratory chamber in 24 overweight women after 4 d of treatment (PPA or placebo) during weight maintenance and after 7 wk of treatment on a hypoenergetic diet (70% of measured baseline 24-h EE). Twelve women (37 ± 2 y, 74 ± 6 kg, 33 ± 1% body fat) were randomly assigned to the PPA group [75 mg osmotic release oral system (OROS)-PPA/d] and 12 (x̄ ± SEM: 38 ± 2 y, 79 ± 1 kg, 37 ± 1% body fat) to the placebo group. Baseline measurements of 24-h EE (7849 ± 226 vs 7834 ± 142 kJ/d), basal metabolic rate (BMR) and 24-h respiratory quotient (RQ) were comparable between PPA and placebo groups. After 4 d of treatment, there was no significant effect of PPA on 24-h EE, BMR, and 24-h RQ compared with placebo. Over the 7-wk diet period, however, the PPA group (n = 8) had greater weight loss than the placebo group (n = 10): −5.0 ± 0.5 vs −3.0 ± 0.4 kg (P < 0.05). The changes in 24-h EE and 24-h RQ over the 7 wk were not different between the groups. We conclude that weight loss is enhanced by OROS-PPA, but this change was not explained by changes in 24-h EE or 24-h RQ. The small number of subjects may have hindered detection of subtle differences in energy metabolism.