Phentermine (Adipex-P, Fastin, Ionamin, Oby-Trim)

Phentermine belongs to the class of drugs known as amphetamines. Amphetamines produce a variety of effects on the central nervous system, including the activation sympathetic nerve pathways and appetite suppression. It is not entirely clear how amphetamines suppress appetite, but their action is similar to biochemical changes during the so-called "fight-or-flight" reaction to stress or danger. During the fight-or-flight reaction, the body switches priorities away from eating or resting toward urgent action. Such a switch involves, among other things, the suppression of appetite. Amphetamines also seem to increase metabolic rate, mostly likely as a consequence of sympathetic nervous system stimulation.

Phentermine was shown to be effective for short-term weigh loss in a number of studies. Unfortunately, in most studies, phentermine was combined with other drugs, so its contribution to weight loss is often hard to determine. Overall, it appears that overweight people taking phentermine tend to lose several kilograms (a kilogram is 2.2 pounds) more than those given placebo (typical duration of such studies was from 2 to 6 months).

Despite a reasonably good evidence of short-term effectiveness, you shouldn't rush blindly to stock up on phentermine. There are significant risks, concerns and side effects you should know about.

First, the effect of phentermine tends to be temporary. The appetite returns in a few weeks even if a person keeps taking the drug. It may be hard to get off the drug without gaining more weight that you've lost. Second, phentermine, like all amphetamines, can cause significant side effects, including nausea, vomiting, cramps, dry mouth, palpitations, high blood pressure and anxiety. It might increase the risk stroke and heart attack in susceptible individuals. Phentermine should not be used in people with hypertension or heart problems, people taking MAO inhibitors and certain other medication. The doctor prescribing phentermine should know your medical history well. Finally, amphetamines, including phentermine, have a known potential for abuse, which may lead to intense psychological dependence and severe social dysfunction.

Therefore, phentermine is not a drug that should be tried casually. Diet and exercise should be attempted first. If diet and exercise prove insufficient, the benefits of using phentermine to jump-start additional weight loss should be weighed against the risks and side-effects.

See also the index of related studies and drug label information for phentermine (Adipex-P).