Consumers Union pans hoodia.The study they mentioned was also the only study I could find in PubMed for Hoodia and makes for very poor evidence of the supplements benefits.
Based on lack of evidence, Consumer Reports on Health (CRH) has
recommended against taking products containing Hoodia gordonii, an
herb that is widely promoted as an appetite suppressant. Hoodia is a
cactus extract said to keep South African tribesmen from feeling
hungry during long hunts. CRH's literature search yielded only two
reports: (a) an unpublished report from a manufacturer about nine
volunteers who were followed for 15 days, and (2) a study in which
the ingredient was injected into the brains of rats. Neither of these
studies substantiates the claims made by hoodia marketers. The
editors also noted that Pfizer had tried to develop hoodia into an
obesity drug but had given up after failing to make an acceptable
synthetic version. [Hoodia: Worth trying for weight loss? Consumer
Reports on Health, Feb 2006]
Increased ATP content/production in the hypothalamus may be a signal for energy-sensing of satiety: studies of the anorectic mechanism of a plant steroidal glycoside.
MacLean DB, Luo LG.
Division of Endocrinology, Hallett Center for Diabetes and Endocrinology, Brown Medical School, Coro Building Providence, RI 02903, USA. firstname.lastname@example.org
A steroidal glycoside with anorectic activity in animals, termed P57AS3 (P57), was isolated from Hoodia gordonii and found to have homologies to the steroidal core of cardiac glycosides. Intracerebroventricular (i.c.v.) injections of the purified P57AS3 demonstrated that the compound has a likely central (CNS) mechanism of action. There is no evidence of P57AS3 binding to or altering activity of known receptors or proteins, including Na/K-ATPase, the putative target of cardiac glycosides. The studies demonstrated that the compound increases the content of ATP by 50-150% in hypothalamic neurons. In addition, third ventricle (i.c.v.) administration of P57, which reduces subsequent 24-h food intake by 40-60%, also increases ATP content in hypothalamic slice punches removed at 24 h following the i.c.v. injections. In related studies, in pair fed rats fed a low calorie diet for 4 days, the content of ATP in the hypothalami of control i.c.v. injected animals fell by 30-50%, which was blocked by i.c.v. injections of P57AS3. With growing evidence of metabolic or nutrient-sensing by the hypothalamus, ATP may be a common currency of energy sensing, which in turn may trigger the appropriate neural, endocrine and appetitive responses as similar to other fundamental hypothalamic homeostatic centers for temperature and osmolarity.
A CBS 60 Minutes News story in November of 2004 reported on the Hoodia plant and it's origins in Africa. The patent holders of the hoodia extract, which was shown to work in their in house studies, claimed that the products with hoodia in it they tested had less than 1% of the actives in the ingredients. This would indicate that most products on the market don't have the necessary standardized ingredients in them to work properly, at least according to the South African company that owns the patent. The active ingredient in Hoodia that is claimed to work is called P57. The pharmaceutical giant Pfizer also attempts to isolate a synthetic version of this ingredient but gave up after it was decided to be too expensive.
So, are there any Hoodia supplements on the market that might actually work? It's hard to say due to the lack of any studies, but most anecdotal reports on the ingredient itself seems to be poor. Hoodia may work best when taken as a standardized extract combined with other ingredients, such as in a product like Dietex. However, all consumers should research for themselves and decide which product is best for them.
Consumer Reports on Health - Hoodia: Worth trying for weight loss? 2/06