Phentermine Hydrochloride

All About Phentermine: The Nation's and the World's Most Widely Prescribed Weight Loss Medication


Photographs of phentermine

Phentermine is the oldest weight loss medication on the US market. It was first approved for prescription sales in 1959. Since then, the drug has been used by tens of millions of people with very, very few serious side effects. Like other currently approved weight loss drugs, phentermine is a mild stimulant.

Trade (Brand) names of phentermine include:

  • Adipex P (Immediate release)
  • Ionamin 
  • Mirapront
  • Obephen
  • Obermine
  • Obestin-30
  • Phentrol

Phentermine is classified as an "appetite suppressant" but interestingly, most of the weight loss that is causes probably has little to do with hunger. In fact, phentermine has other effects that cause weight loss including increasing metabolism and increasing satiety.

Phentermine, Brown Fat and Thermogenesis

Phentermine is a "non-selective beta-3 alpha adrenergic agonist". This means that it binds to protein receptors called "beta-3 receptors". These proteins are found in certain special fat called "brown fat" and when phentermine activates those cells, they are triggered to burn-off body fat to produce heat. The production of heat from brown fat is called "thermogenesis" (literally "heat creation"). This is one of the ways that phentermine causes weight loss.

Phentermine Increases Satiety

Satiety is feeling of fullness that happens when we eat that makes us stop. Phentermine causes this feeling to happen earlier in a meal with less food than normal. 

Phentermine and Appetite

Phentermine is called an "appetite suppressant" but it probably shouldn't be. That's because it doesn't reliably suppress appetite. Many people who take phentermine for weight do NOT notice that they feel less hungry. On the other hand they usually still lose weight and do report that despite being hungry BEFORE eating, they fill up more quickly on less food.

Phentermine and Weight Loss

Phentermine is a weight loss medication that works, as explained above, by increasing heat output and satiety. It really works.

Tolerance to Phentermine

The reason that phentermine is not a miracle is because every person who takes it slowly develops partial tolerance or resistance to it effects. That means that while it may seem very effective at the start of therapy, it generally seems less so after several months. Unfortunately this tolerance is universal (everyone who takes phentermine gets it) and the only way to lose the tolerance is to stop taking the medication. Let me also be clear that the tolerance is NOT total and even in the long-term, phentermine still does work, but not as well.

Safety of Phentermine

All drugs have risks. Phentermine does too but in the broad scheme of medicine, they are relatively rare and usually not serious. If yo want to read more about this here is our page on the safety of phentermine.
Subpages (1): Phentermine