Diet and Health FAQ

Tagged As: Diet Pill Information

Question:
Can someone explain to me the mechanism by which diet pill work? I know they suppress the appetite, but how? Also, are there side effects?

Answer:
Well, their mechanism of action isn't particularly well understood. Part of it seems to come from reduced food intake, but an increase in metabolism may contribute to their effects on body weight as well. Almost all anorectic drugs are sympathomimetic amines, chemicals which mimic in one way or another the actions of the neurotransmitters dopamine, epinephrine (adrenalin) or norepinephrine. The prototypical drug of this class is amphetamine and its active isomer dextro- amphetamine. This drug causes stimulation, euphoria, talkativeness and also suppresses appetite, at least for a few weeks. There are various derivatives of dextroamphetamine which were originally purported to have fewer side effects than amphetamine, but that is mostly because they're less potent and less powerful than dextroamphetamine. These would include diethylpropion, phentermine, benzphetamine, mazindol, phenmetrazine and phendimetrazine. Over-the-counter diet pills in the USA contain another amphetamine analogue, phenylpropanolamine, better known as a nasal decongestant. It has few stimulant effects on the central nervous system (it doesn't cause insomnia or euphoria), but it can raise blood pressure, especially in people who are borderline hypertensive already. One sympathomimetic amine which is a bit unusual in that it doesn't which doesn't seem to work in the way others do is fenfluramine and its active isomer dexfenfluramine. It seems to act on serotonergic pathways, promoting release and reducing reuptake of the neurotransmitter serotonin. It causes sedation, doesn't cause euphoria in recommended doses, and doesn't have many overt sympathomimetic effects such as an increase in blood pressure. The racemic mixture has been sold for 25 years in the US under the tradename Pondimin. The dextro isomer is presently being considered for FDA approval; it's already sold in Europe. All of these drugs will cause a modest weight loss of about 10% of initial body weight which is sustained for as long as the drug is continued. When the drug is stopped, the lost weight invariably comes back. The effects of these drugs are similar to the effects of smoking on weight. Smokers are usually 5-10 pounds lighter than nonsmokers, and quitting smoking often causes people to gain weight.