Modafinil (Provigil) has been suggested as a potential wake-promoting drug that might be helpful in PWS. Interestingly, this article (although a very small study) showed that individuals taking modafinil consumed less food. Compared to amphetamine, which also increases wakefulness and decreases appetite, modafinil did not cause increased heart rate at high doses.
Wake-promoting agents with different mechanisms of action: comparison of effects of modafinil and amphetamine on food intake and cardiovascular activity . Makris AP, Rush CR, Frederich RC, Kelly TH. Appetite. 42:185-95, 2004.