Participants will then attend three weekly study visits, starting 1 week after completing screening. At each visit, participants will receive a dose of either betahistine or placebo. The dose of betahistine will increase at each visit, starting at 50 mg, then increasing to 100 mg, and then to 200 mg. Participants will be asked to refrain from eating and to drink only water in the 12 hours prior to study visits. Also at each visit, participants will have their vital signs measured, complete questionnaires concerning appetite and mood, perform attention and memory tests, provide several blood samples, undergo an EKG test, and perform a breathing test. Some of these tests will be repeated several times over the course of each study visit. Additionally, at the last study visit, participants will undergo a physical examination and provide urine samples.