In
1999, the drug orlistat was approved by the Food and Drug
Administration (FDA) as an obesity treatment. Orlistat works by
reducing the body's ability to absorb dietary fat by about one third.

Most currently available weight-loss medications are approved by the
U.S. Food and Drug Administration (FDA) for short-term use, meaning a
few weeks or months. Sibutramine and orlistat are the only weight-loss
medications approved for longer-term use in significantly obese
patients, although the safety and effectiveness have not been
established for use beyond 1 year. While the FDA regulates how a
medication can be advertised or promoted by the manufacturer, these
regulations do not restrict a doctor's ability to prescribe the
medication for different conditions, in different doses, or for
different lengths of time. The practice of prescribing medication for
periods of time or for conditions not approved is known as "off-label"
use. While such use often occurs in the treatment of many conditions,
you should feel comfortable about asking your doctor if he or she is
using a medication or combination of medications in a manner that is
not approved by the FDA. The use of more than one weight-loss
medication at a time (combined drug treatment) is an example of an
off-label use. Using weight-loss medications other than sibutramine or
orlistat for more than a short period of time (i.e., more than "a few
weeks") is also considered off-label use.
Reference:
National Institute of Diabetes and Digestive and kidney