Anti-obesity drugs include all pharmacological treatments intended to reduce or control weight. Because these drugs are intended to alter one of the fundamental processes of the human body, anti-obesity drugs are medically prescribed only in cases of morbid obesity, where weight loss is life-saving.

Anti-obesity drugs operate through one or more of the following mechanisms:

• Suppression of the appetite.
• Increase of the body's metabolism.
• Interference with the body's ability to absorb specific nutrients in food. For example, Orlistat.

Anorectics (also known as anorexigenics) are primarily intended to suppress the appetite, but most of the drugs in this class also act as stimulants (dexedrine, e.g.), and patients have abused drugs "off label" to suppress appetite (e.g. digoxin).

Some anti-obesity drugs have severe and often life-threatening side effects. (See, for example, Fen-phen.)

Because the human body uses various chemicals and hormones to protect its stores of fat (a reaction probably useful to our ansectors when food was scarce in the past,) there has not yet been found a 'silver bullet', or a way to completely cucrumvent this natural habit of protecting exess food stores. Because of this, anti-obesity drugs are not a practical long-term solution for people who are overweight.