Phentermine ( A.K.A. Adipex-P; Obenix; Oby-Trim; Anoxine-AM; Fastin; Ionamin; Obephen; Obermine; Obestin-30; Phentrol) is a powerful drug first approved by the FDA in 1959. In use for almost half a century, it has been a source of much controversy since the late 1990s.

Phentermine works by triggering a fight-or-flight response. It acomplishes this by changing the Seratonin levels in the brain and releasing Adrenaline and other related chemicals. This can result in, among other things, heightened blood-pressure, a feeling of panic, insomnia (or, in some, drowsiness) and a loss of appetite.

It is only recommended for moderate weight-loss and for short-term use. It is known to be dangerous for people who already suffering from high blood-pressure or Glaucoma. It can be addictive, and abruptly quitting ("cold turkey") has been known to cause lethargy, depression, and similar related conditions. Some other known side effect include changes in insulin requirements as well as impotence.

Sources:
http://en.wikipedia.org/wiki/Phentermine [Wikipedia]
http://www.medicinenet.com/phentermine/article.htm [Medicine Net]
http://www.fda.gov/cder/news/phen/fenphenqa2.htm [FDA.Gov]
http://www.nlm.nih.gov/medlineplus/druginfo/medmaster/a682187.html [Medline Plus]
http://www.Health-Hack.com/ [Health-Hack.com]