 In pediatric gastroenterology practice, cyproheptadine is the most commonly used drug for appetite stimulation, weight gain, and feeding intolerance in younger children with feeding disorders. A first generation histamine and serotonin antagonist, cyproheptadine is thought to promote appetite stimulation and weight gain by increasing insulin-like growth factor-1 IGF-1 concentration. It may also interact with receptors in the ventromedial hypothalamus and exert hormonal effects. While the exact mechanism of action is still being investigated, several studies have evaluated the benefits of cyproheptadine in select patient groups, including patients with cystic fibrosis, cancer, undernourished children, and children with feeding disorders. These studies have all reported that cyproheptadine promotes weight gain and stimulates appetite. Reported side effects of cyproheptadine in these studies are primarily related to drowsiness which tends to significantly improve or resolve within two weeks of use. Another undesired effect is the development of drug tolerance, i.e. tachyphylaxis. To avoid this, it is common clinical practice to cycle on and off the medication a few weeks each month. 