Related Study at McLean Hospital: If you would like to participate in this study of glycine versus placebo at the Freedom Trail Clinic, the investigators will ask you if you would also like to participate in a related study at McLean Hospital. The study at McLean Hospital will look at the effects of glycine and placebo on levels of glycine in the brain. The study will use magnetic resonance spectroscopy to measure brain glycine levels. The magnetic resonance (MR) scanner looks like a large cylinder with a tube running down the center. You will be asked to lie down on your back on a foam-padded table and place your head into a special holder. The table will slide you inside the "hole" of the scanner. Soft foam rubber sponges may be placed on both sides of your head for comfort and to help keep your head from moving. Because the scanner contains a strong magnet, you will be asked to remove all metal objects from your person including, but not limited to: watches, rings, necklaces, bracelets, earrings and other body piercings, belts, loose change, wallet (with credit cards), items of clothing containing magnetic materials (for example, underwire bras, certain types of zippers), and shoes. These items will be secured in a safe place until your scan is completed. You will be able to remain in your street clothes. The investigators will ask you if study staff from McLean Hospital can contact you to tell you more about the study. You may refuse to be contacted by McLean Hospital. However, if you do not participate in the study at McLean, you are not eligible for the study here at the Freedom Trail Clinic.