The sample size is calculated by the software PASS 11.0. The alternative hypothesis set as Mean 1<Mean 2, which means that the participants in the entacapone group loss more weight than the participants in the placebo group. Because this is a pilot study, the error is set as (1-β)=0.8 and α=0.1. According to the results of the study on tesofensine, another weight loss drug, participants in the entacapone and placebo group are estimated to loss 2 kg and 10 kg respectively. The estimated sample size is 30, 15 in each arm.