By Donna Feldman, MS, RD

If you think the lure of diet pills is a new phenomenon, think again. Consider Dinitrophenol. Sounds like an explosive chemical, right? Wrong. It was the first diet pill, sold in the 1930s with the promise of burning off extra calories by increasing metabolism. Actually it was explosive. The increased metabolism gave people strange fevers, which caused plenty of nasty side effects, including death. Unfortunately, the diet pill industry has not progressed much since then. Meanwhile the obesity epidemic has exploded, making the promise of magic even more appealing to unwary consumers.

Two groups of diet pills

Diet pills come in two basic groups: over-the-counter and prescription. The main difference is regulation. Prescription formulas are heavily researched and tested for effectiveness and safety. Over-the-counter preparations, on the other hand, need no research. Many are formulated according to the latest diet and herb fads.

Prescription diet pills: no guarantees

Despite all the mandatory testing, prescription weight loss drugs have a mediocre track record. Weight loss is 10-20% over a year. And healthy diet and exercise are essential parts of the plan. Prescription weight loss drugs do not magically melt away fat by themselves.

Many people remember "fen-phen" from 10 years ago. This drug combination worked in the brain by decreasing appetite and increasing a sense of fullness. But "fen-phen" was linked to heart problems in some users, and was withdrawn from the market. What's left? Sibutramine (Meridia) works similarly, increasing the sense of fullness and cutting food intake. But weight loss results are modest, and sibutramine can cause side effects, including increased blood pressure and heart rate.

Orlistat causes malabsorption of dietary fat. Theoretically you could chow down on a large order of fries or a double scoop ice-cream cone and not worry about all those fat calories. But fat malabsorption causes orlistat's embarrassing side effect--"leakage," or diarrhea. The more fat calories you ingest, the worse the problem is. For dedicated dieters, orlistat could work by enforcing a very low fat diet, and reducing calorie intake. For the less dedicated, this drug is more trouble than it is worth.

Over the counter diet pills: no guarantees

There is a widespread belief that over-the-counter diet pills must be safe and effective or they would not be on store shelves. This is false. Regulation only seems to come after a preparation causes serious problems. Ephedra was once used in many diet pills, until it was linked to users' deaths, and taken off the market. Diet pill manufacturers quickly created new formulas.

These days, most contain some combination of green tea extract, caffeine, and tiny amounts of herbs and/or vitamins. The pills are promoted with catchy names like Cortislim or Trimspa, photos of muscular models, and websites with testimonials and success stories. But read the fine print: None of these formulas claim to magically cause weight loss alone. Diet and exercise recommendations are prominent features on the product websites.

What about Hoodia?

Hoodia is an extract from a plant native to Africa, supposedly used by indigenous people as an appetite suppressant. Dieters are always looking for appetite control, and some over-the-counter diet pills now contain Hoodia--or claim to contain it. In fact, the plant is endangered, and export requires special permits. Whether "Hoodia" on the label means real Hoodia is in the pill is not clear. Buyer beware!

...and Alli?

A new over-the-counter pill from a major drug company, Alli, is a version of prescription orlistat. It causes fat malabsorption, and will only lead to weight loss when combined with a low-fat diet and exercise plan. The official Alli website makes it clear that the user must follow a diet for success. This is a relatively new approach to marketing diet pills. Instead of promising magic, Alli is being marketed as just one piece of a weight-loss lifestyle.

Conclusion: there is no overnight weight loss formula with no side-effects

The Holy Grail of diet pills is a formula that melts fat overnight, with no side-effects. This is not going to happen. However, consumers will continue to hope for magic. When considering diet pills, keep one thing in mind: If any of these pills truly worked, why is the obesity epidemic getting worse?