There are all kinds of facts and information available about hoodia gordonii on the internet. Some of the claims are factual and other claims quite controversial. Let us sort out these facts and claims and find references where possible.
Let’s take a look at some of the facts. There are many species of the hoodia plant (a succulent, not a cactus) that grow wild in Southern Africa, but only one species hoodia gordonii, is believed to naturally suppress hunger and thirst. For centuries, the Bushmen or San people of Southern Africa have used the flesh of the hoodia gordonii plant to suppress hunger and thirst before embarking on long hunting expeditions. During the 60s, scientists at the South African CSIR (Council for Scientific and Industrial Research), began to study hoodia gordonii. Working together with a British company, Phytopharm, they isolated an active ingredient in hoodia gordonii – now known as P57 – which they believe is responsible for suppressing appetite and patented it. P57 was injected into the brains of laboratory rats and it was noted that it had a direct effect on the hypothalamus, which controls hunger, thirst and blood sugar levels in the body. The laboratory animals did lose weight. The hoodia gordonii plant only grows in Southern Africa (attempts to grow this wild plant in the deserts of America and Mexico were not successful), it is now a protected species and it takes 5 to 7 years for the plants to mature enough for the P57 to be extracted from them.
Now for the claims. The flesh of the hoodia gordonii plant certainly does suppress appetite as proven by the bushmen of the Kalahari Desert. But as the plant itself cannot survive export, it is the extract P57 that is used by various companies marketing hoodia gordonii as an appetite suppressant and the clinical trials (using people, not rats) are still in progress. The dosage required to produce the result needed has not yet been quantified, so how the manufacturers of various hoodia gordonii products have come to their conclusions is not known. As yet, there is no research available recommending dosage guideline. It is only because it is being sold as a supplement and not as a prescription drug that it has gotten away without having to furnish any kind of clinical study as back-up and with huge claims, the manufacturers are raking in the money.
All clinical research done on hoodia gordonii comes from Phytopharm and its partner companies, Pfizer and now Unilever. Phytopharm has an FAQ page on their website and anyone interested in the history of hoodia gordonii will find a lot of information there. You can also find a lot of information on other hoodia websites.