Professor Lesley Regan tested the pill, costing just pennies to make from ingredients found in any kitchen, as part of a TV show that lifts the lid on the diet and supplement industry.
Regan showed that volunteers testing the dummy pill lost up to half a stone in six weeks, without such unpleasant side effects as are associated with the medicines available over the counter.
Those trying the pill were asked to take it three times a day before eating, to stick to a healthy diet and keep active.
These are the same routine advices that are given with most weight-loss aids.
One Cassie Basham, a 39-year-old mother-of-four from Newmarket, Suffolk, weighed 14st 7lb when she signed up for the study.
She admits that she was desperate to try the pill.
"We were told the pill would reduce the fat molecules in our body. I was still eating my normal food, but a little bit less of it," the Sun quoted her as saying.
"I never felt hungry and didn't get the urge to snack on crisps or biscuits," she added.
She revealed that she lost 7lb, dropping a dress size in the six-week trial, and she is presently down to 13st 5lb.
"I was stunned when I found out the pill was simply a placebo. It genuinely reduced my appetite," she admitted.
Prof Regan says: "There are so many products packaged around a 'magic ingredient' that is supposed to have special weight-loss powers. There is no quick fix. The key to sustained weight loss is eating the right things, taking enough exercise and increasing your metabolic activity in little ways."