Melatonin, a medical product with many faces

Most people encounter difficulty sleeping or other forms of discomfort when their biological clock is disrupted, for example with jet lag. The hormone melatonin is responsible for regulating our circadian rhythm (i.e., our daily sleep/wake cycle, also known as the biological clock), and this hormone is also used in various forms to provide for relief. What are the benefits and risks of taking melatonin, and how might they relate to regulatory control?