It was after the CSIR (the Council for Scientific and Industrial Research in South Africa) leased their patent on Hoodia to Phytopharm that the real in depth of Hoodia could start.
The active ingredient in Hoodia Gordonii, now known as P57, copies the effect that glucose has on part of the brain,specifically the Hypothalamus.
The Hypothalamus controls your appetite. As you eat, the glucose from the food cause the body's glucose levels to rise. The Hypothalamus notes these changes, and then at what it regards to be a suitable time, sends a signal to stop eating.
The active P57 Hoodia molecules mimics the glucose effect, but to a dramatically higher degree. This is why the San tribes people used Hoodia, to 'fool' their body in to believing they were full while on hunting trips so they wouldn't eat their catches on the return journey.
In 2001, Phytopharm conducted a double-blind, placebo controlled clinical study. A group of healthy but overweight volunteers were put in to a 'phase 1' unit. All they could do was eat, read, or watch television - no exercise allowed!
After 15 days the volunteers taking the Hoodia P57 had not only eaten less, they had lost significant body fat compared to the control group taking the placebo. In fact, the P57 group had cut their daily food intake by between 1000-1500 calories a day. Plus this was achieved without any members of the group feeling hungry.
Other 'private studies' (by Hoodia supplement manufacturers), are confirming these findings, along with the suggestion of an increase in energy and stamina (another reason that the San tribes people would have taken Hoodia).