LAS VEGAS -- It's the latest diet craze to hit the valley.

With a couple of drops under the tongue, patients drop weight.

It's called HCG, a hormone women produce when they're pregnant.

Several doctors in town are now prescribing HCG to help people shed hard-to-lose pounds.

Women and men are lining up to give it a try, but one doctor has a word of warning.

“What that does is changes your metabolism … It gives your body access to its own fat stores," said Dr. King Rolands, a Las Vegas chiropractor who is offering the HCG program.

He is opening a “health recovery clinic” that includes yoga and weight loss programs, including HCG.

"This is for the person who tries, really, really hard to lose weight, and every time they lose weight, after they get off the diet, they gain an extra 10 pounds," Rolands said.

HCG is supposed to work by making the body think it's pregnant, man or woman. Since a fetus needs food, the theory is, the body will utilize its fat stores and to help lose weight.

"I felt like I sneezed, and the weight came off," said Larae Brown.

Rolands recruited Brown, his sister, to help run the weight loss program. She's a diet counselor from Utah, where she started using HCG.

"So, when I came to work at the clinic that I work at now, it was cool. I went on the HCG, and in 21 days, I lost 16 pounds," Brown said.

HCG is only half of it. In addition to a couple of drops of HCG under the tongue or injected, patients have to adhere to a strict diet, just 500 calories a day. That means small meals like 3.5 ounces of chicken, a vegetable like cucumbers, Melba toast and fruit.

"It is really weird to think 500 calories a day could be so easy," said Brittney Schriever, who lost weight using HCG.

She started taking HCG on the advice of her mother, who had great success with it.

“I was on the HCG diet for five weeks, and I lost 38 pounds. And now, I've been maintaining for three weeks," Schriever said.

She said the first two days were difficult, because she felt like she was not eating enough.

“Does this HCG help those 500 calories? I doubt that. There is no evidence it makes the low calorie diet any safer," said Dr. Fred Toffel, an endocrinologist.

He said HCG is not FDA approved for weight loss, and there are no studies in mainstream scientific literature that prove it's safe or that it helps you slim down.

"We don't know. It may be fine, but so is taking a glass of water fine, but it's not benefiting you. But I bet it's costing you plenty. So, buyer beware. If it's too good to be true, it probably is," Toffel said.

Rolands stands by HCG. He said he's used it himself and thinks of it as a “useful tool” in a “losing battle.”

Schriever said she's beginning the next phase of the diet and now has the incentive she needs to persevere.

"To drop two sizes in a month … are you kidding? That's awesome," she said.

Only a medical doctor can prescribe HCG.

There are at least three doctors prescribing the hormone for weight loss in the valley.

Since Rolands is a chiropractor, he refers patients to a physician next door.

As far as the cost, it depends on the medical tests needed.

One vial of injectable HCG costs about $55.

Both Rolands and Toffel said anyone with active cancer should not use HCG, because it is a mild growth hormone.