After you have completed the initial assessment, you will begin taking the study medication. The study medication is glycine or identical placebo and is in the form of a liquid. A one-week supply of the medication will be given to you on your weekly visit to McLean Hospital. You will take one dose of medication with breakfast in the morning and the second dose of medication with dinner in the evening. You should keep the study medication refrigerated. You will take approximately 30 grams (about 1 quarter of a liter) twice per day for the first 6 weeks, but the exact amount that you will take will depend upon your weight. We will instruct you in exactly how much to take.