There are no field studies looking at the effects of MPH on food intake (neither as a main outcome nor secondary outcome). Therefore, our only way of estimating effects sizes is extrapolating from our previous laboratory studies. In a laboratory study by the investigators, an effect size of .93 was attained in 9 obese adult males for the primary outcome of food intake with mean energy intake in kilocalories for MPH (0.5 mg/kg) and placebo of 843.5 + 393.4 and 1095.9 + 271.1, respectively. In a second study in 14 normal weight adult males and females, an effect size of .69 was attained, favouring MPH (0.5 mg/kg) for food intake in an ad libitum buffet meal with mean difference in kcals of -133 (1099 for MPH minus 1232 for placebo), with a standard deviation of 192.0 kcals for the paired differences based on t-tests. Based on the more conservative effect size of .69, it would be possible to detect a significant difference in kcals consumed over a 60-day period between MPH and placebo using a paired t-test with an alpha of 0.05, power of 0.80, with 18 participants per group. Thus, the plan to include 40 participants per group should enable the investigators to look at trends on other energy balance (secondary outcome) variables, accounting for an expected drop-out of 5-10%. The plan is to run 3 new participants/month, thus the experimental part of the study should last approximately 14 months.