"Hoodia, a plant that tricks the brain by making the stomach feel full, has been in the diet of South Africa's Bushmen for thousands of years."*Quote from About.com story: "Hoodia may work right away, or may take several weeks. Key results of hoodia reported include a reduced interest in food, delay in the time after eating before hunger sets in again, feeling full more quickly, and a general feeling of well-being."
*Quote from BBC News story: "What the Hoodia seems to contain is a molecule that is about 10,000 times as active as glucose. It goes to the mid-brain and actually makes those nerve cells fire as if you were full. But you have not eaten. Nor do you want to."
It works by making patients feel full after ingesting it, and the company says it has been shown to lower food intake by 30-40% in a small study just completed."