Additional Study Information: Growth hormone and insulin-like growth-factor 1 (IGF-1) are two hormones that are very important to human growth and metabolism. In disorders of GH and IGF-1 excess and deficiency, significant growth and metabolic abnormalities can develop. This study investigates the effects of GH on the appetite-stimulating hormone AgRP (agouti-related peptide) and the effect of the weight loss medication "Liraglutide" on AgRP. This study is open to healthy subjects and patients with known GH deficiency who are between the ages of 18 and 45. Study participants will be asked to come for a screening visit and 6 study visits over the course of 4 treatment arms of 28-days each. In each treatment arm, participants will take, in random order, nightly injections under the skin of GH, liraglutide, GH and liraglutide or placebo. Treatment arms will be separated by 8 weeks. Tests to be done include blood sampling, body composition assessment by MRI, energy expenditure testing and recording of diet and activity. The complete study participation duration will be 10 months. Participation in this study will help advance our understanding of these hormones and their effects on growth and metabolism. Contact Rosa Lazarte 212-305-4921 or rl2345@cumc.columbia.edu.