Alli® is an over-the-counter weight loss supplement that is a component of the Alli diet plan. The supplement sufficiently facilitates weight loss when combined with a low-fat, low-calorie diet. However, the complete Alli diet program is designed to incorporate an online support system that includes menu planning and networking with dietitians and other dieters. In fact, the manufacturer, GlaxoSmithKline, refers to the product as “a pill with a plan.” The key difference between this and similar programs is that the Alli diet pill is the only non-prescription supplement approved by the U.S. Federal Drug Administration for weight loss at this time.

The science behind the Alli® diet pill is quite simple. The active ingredient is orlistat, the same substance found in the prescription weight loss medication Xenical®, but in a lower concentration. This agent is a lipase inhibitor, meaning that it targets and binds to pancreatic lipase, the enzyme produced by the pancreas. When transported to the intestines, this enzyme breaks down lipid fats, such as triglycerides. However, when this action is blocked, the fats remain undigested and are not absorbed by the body.

The inhibition of lipase activity results in approximately 25 percent of dietary fat intake being redirected for elimination rather than absorption, as well as reduced calorie intake. However, the Alli® diet pills must be taken at mealtimes in order for this to occur. In addition, success depends on each meal providing the near equivalent of 15 grams of fat. Otherwise, higher amounts of fat may produce what the manufacturer calls “treatment effects,” which include gas and loose stools.

A daily multivitamin is recommended while taking the Alli® diet supplement since it also tends to block absorption of several fat-soluble vitamins, including A, D, E, K, and beta-carotene. In addition, this product is not intended to be taken while consuming a diet low in carbohydrates. It is also not intended for women who are pregnant or nursing.

Aside from the small percentage of people who left the program during clinical trials due to “treatment effects,” the Alli® pill is considered safe and without significant side effects. Unlike many other weight loss supplements, the product does not impact the heart, brain or central nervous system. As such, there is little or no risk of disturbed sleeping patterns, nervousness, or heart palpitations while taking this product. However, certain medical conditions may cause complications. In fact, a consultation with a physician is recommended prior to taking Alli® for people who have had their gallbladder removed, gastric bypass surgery, or those with a history of pancreatitis or kidney stones.