BOSTON -- A new diet that claims to help you lose as much as three pounds a day is generating controversy in the medical community.

It's called the HCG diet, and it is getting a lot of attention online.

The experts say there are no short cuts: to lose weight and keep it off you need to exercise and diet. Now, they are warning against a controversial fad diet that promotes big results by using a so called 'magic potion.'

Photographer Judy Carey loved taking pictures, but she hated having hers taken until she dropped from a size 14 to a size 6.

"I lost 43 pounds total and feel great," Carey said.

She said she did it by rubbing a little cream on her wrist daily. The magic ingredient: human chorionic gonadotropin or HCG.

"HCG is human chorionic gonadotropin. It's the pregnancy hormone," said Dr. Robert True

True said the hormone that helps insure that a developing baby gets enough calories in the womb can work wonders on the waistline of women trying to diet.

Some infertility experts are horrified.

"It can also be very dangerous. What worries me is this is a hormone and we know that when we mess with hormones you can really mess with people's health," said infertility expert Dr. Alice Domar.

The way the diet works is, dieters go on a 500-calorie-a-day diet. Then they inject HCG or rub it into their skin to lose weight without feeling hungry..

"And if (your system) thinks you are pregnant, it's going to force your body to pull the nutrients from the stored areas of fat in your body," True said.

It sounds simple, but Domar has concerns.

"You can not meet your nutritional needs on 500 calories a day. It seems dangerous," Domar said.

Karen Weaver said she lost 13 pounds in 20 days without feeling tired while using HCG.

"It is the easiest diet. I never thought that when he told me that when I would be eating 500 calories a day that I could do it," Weaver said.

Web sites are filled with testimonials and unregulated HCG products for sale, but look a little deeper, Domar said, and you will find many reputable studies have called the diet "ineffective" and "worthless."

"Everybody wants to lose weight. Nobody wants to be hungry. But you don't want to lose weight in a way that jeopardizes your health," Domar said.

Despite decades of negative findings, the HCG diet was popularized in a 2007 book. The author has been previously targeted by the Federal trade Commission for allegedly promoting unproven cancer cures and other products.

Experts say: stick to the tried and true to lose weight -- hit the gym and eat right.