11.   Also prescribed for weight loss is phentermine, a stimulant that affects two brain messenger chemicals, dopamine and norepinephrine, that contribute to alertness.

12.   All three drugs work by changing the levels of brain chemicals that influence appetite and cravings.

13.   All work by changing levels of a brain chemical called serotonin, a substance involved in the modulation of many brain states, including depression, euphoria and appetite.

14.   Dopamine is a brain chemical that regulates movement, attention, pleasure and motivation.

15.   Ecstasy appears to act on the parts of the brain that regulate the production of serotonin, a brain chemical linked to mood and emotions.

16.   Endorphins, naturally occurring brain chemicals, are similar to the opiate morphine.

17.   For more than a decade, scientists have known that a brain chemical called NPY, for neuropeptide Y, stimulates appetite.

18.   Her research has identified certain biological signals that affect the synthesis of these brain chemicals.

19.   How Zyban helps people quit smoking is unknown, though the presumption is the drug affects two brain chemicals, dopamine and norepinephrine, linked to nicotine addiction.

20.   If it does help, it may do so by increasing dopamine, a brain chemical, says Tyler of Purdue.