With so many diet pills claiming to offer ?guaranteed results? and ?massive weight loss?, it has become difficult to ascertain which diet pill is actually effective. To better understand which diet pill is effective and which one is not, it is important to know the various diet pills available in the market.

Prescription diet pills

Prescription pills like Meridia and Xenical are some of the few diet pills that are available only on a doctor's prescription. The sale of Meridia and Xenical is regulated closely by the FDA and requires patient's to meet certain criteria before they can be prescribed Meridia or Xenical.

Over the counter diet pills

Although the FDA has recently approved a few drugs to be added to the list of over the counter diet pills, there has been considerable debate over which drugs should be sold over the counter. Till 2000 over the counter diet pills contained a substance called PPA (phenylpropanolamine), but recent studies have pointed out that PPA can increase the risk of a stroke and very few over the counter drugs now contain PPA.

Herbal diet pills

The number of herbal diet pills available in the market exceeds the number of prescription and over the counter drugs available. Herbal diet pills are usually a combination of various botanical extracts like Hoodia, bitter guard, bitter orange and green tea. The effectiveness of herbal diet pills is still unclear, and no single herbal diet pill has been proven effective in inducing weight loss. In addition, various metals like chromium have also been used in diet pills but the truth is that the effectiveness of herbal diet pills is still unproven.

How do diet control pills work?

Prescription diet pills use various mechanisms to help a person loose weight. Prescription diet pills like Meridia , Tenuate and Fastin affect the hypothalamus which is responsible for regulating the feedback mechanism that controls the stomach's feeling of being ?full?. In essence, a person feels full with a relatively small meal or sometimes without eating anything at all. Other prescription diet pills like Orlistat inhibit the action of an enzyme called lipase which is responsible for breaking down fat in the body. Diet pills like Orlistat are responsible for inhibiting the action of Lipase thereby reducing the absorption of lipids (fats) in the body.

Most herbal diet pills are designed to decrease an individual's appetite and thereby reduce their daily calorific intake. Although various herbal diet pills claim to be effective and ?guarantee? results, very few herbal diet pills have undergone clinical testing to establish their effectiveness. On the other hand, OTC (over the counter) diet pills contain caffeine and other synthetic substance like synephrine that supposedly increase the metabolic rate of the body, thereby increasing the rate at which calories are burned up by the body.

In essence, different diet pills have different mechanisms for helping people loose weight. What is equally true is that not all diet pills are as effective as they claim they are.

What are the side effects of diet pills?

Lipase inhibitors like Orlistat remove unabsorbed fat through the intestine and common side effects of consuming Orlistat include cramping, gas and diarrhea. In addition, people using diet pills like Orlistat are also advised to consume multivitamins as lipase inhibitors also reduce absorption of vitamins. People using diet pills like Meridia are advised to look out for common symptoms like high blood pressure and increased heart rate. In fact, people with existing heart problems are usually advised not to use diet pills like Meridia (as sibutramine has a tendency of interfering with the normal functioning of the heart). There is a misconception that herbal diet pills are safe, and even ?all natural? diet pills have various side effects like diarrhea, constipation etc.

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