Hoodia diet pills and their bottle. These pills purport to contain extracts of Hoodia gordonii, a cactus found in the Kalahari desert that has been used by tribesmen for thousands of years to stave off hunger. Chemical analysis found a molecule, named P 57, that acts on the brain's hypothalamus to suppress appetite. It acts on the same receptors as glucose, but is about 10,000 times as active. In clinical trials it decreased the daily calorie intake of obese people by up to 1000 calories. The pharmaceutical company Pfizer, which holds development and marketing rights for the plant, is undertaking more trials. Tests of Hoodia pills currently on the market have found zero trace of the extract in the pills.