Q. Can hoodia make me eat less?

A. Hoodia is being promoted as the latest "miracle" appetite-suppressing weight-loss product. Sold in capsule, liquid and tea form, it's one of the main ingredients in TrimSpa and other diet supplements.

A cactus-like plant, hoodia grows in the Kalahari Desert of South Africa. For centuries, the region's indigenous tribesmen have chewed the plant's stalks to curb hunger during long hunting trips when food was scarce. Many types of hoodia exist, but only hoodia gordonii is believed to suppress appetite.

In 1963, South African researchers discovered that hoodia caused weight loss in animals. In the 1990s, the plant's active ingredient was isolated and patented as P57. The British company Phytopharm has an exclusive license to develop P57 into an appetite-control drug.

In a study by Phytopharm, the only one done on humans so far, men who took P57 cut back on calories and lost body fat. Unfortunately, it was never published. Published research on hoodia is scarce.

Researchers at Brown University found that hoodia affects cells in the part of the brain responsible for appetite. It fools the brain into thinking that there is enough blood sugar, triggering the brain to turn off its hunger signals.

Many products that contain hoodia also are full of caffeine-containing stimulants such as guarana, orange peel and tea extracts that increase urine flow, resulting in water-weight loss. They often contain other unproved weight-loss ingredients as well.

Even if chewing on the fresh hoodia plant suppressed hunger in South Africa's tribesmen, that doesn't mean hoodia supplements will have the same effect. Supplements now being sold don't even contain the patented active ingredient, P57. And even if a product is labeled 100 percent hoodia, you have no way of knowing if you are getting the right plant species, or even the right part of the plant.

It is not known whether regular, daily use of hoodia is safe. The South African tribesmen used it sparingly and not as a means to lose weight. Recently, a researcher from pharmaceutical giant Pfizer (which pulled out of a sublicense to develop hoodia) cautioned that "unwanted effects on the liver" have been observed. For now, the safety and effectiveness of hoodia remain to be proven.