A new prescription diabetes drug that has only been on the market for nine months, Byetta (exenatide), is attracting a rapidly growing following because of its effectiveness in helping those taking it lose weight.

First in a class of medicines that "mimic" the effects of naturally occurring hormones from the intestines, Byetta (pronounced bye-A-tuh) was approved by the FDA last April to help improve blood sugar control in adults with type 2 diabetes.

But the big news about Byetta, which has led to an unexpected surge in sales even though it is not even being marketed yet directly to consumers, comes from stories of how it has helped diabetics taking it shed significant amounts of weight.

Rev. John L. Dodsona, 73, of Felton, CA, told the New York Times he has lost almost 60 pounds since starting Byetta last June and now weighs 178, his lowest weight since college.

Karen Brady, 51, told the newspaper she has lost 50 pounds in the last five months on Byetta and weighs 150 pounds.

While these results are surely the exception, researchers reported that in the three clinical trials that led to the drug's approval, diabetic participants taking Byetta lost an average of 3 percent of their body weight during the first 30 weeks of the trial.

Researchers subsequently reported at the American Diabetic Association scientific meeting last summer that weight loss had continued for many trial participants out to 82 weeks, and had been accompanied by a significant drop in their triglycerides and an increase in their HDL (good) cholesterol.

The company's marketing Byetta, Amylin Pharmaceuticals and Eli Lilly, insist the drug is only for the millions of Americans with type 2 diabetes, and say they strongly discourage use of Byetta by non-diabetics as a diet drug.

Unlike the weight-loss drug Acomplia (rimonabant), which has been the subject of clinical trials involving both diabetic and non-diabetic patient groups, Byetta has not been the subject of any clinical trials involving non-diabetics. And at this point, no Byetta trials as a weight-loss drug for non-diabetics are planned.

But a drug that has been approved by the FDA for one use can be prescribed "off-label" for other uses, and some doctors are believed prescribing Byetta as primarily a weight-loss aid for patients with normal blood sugar.

The drug's active ingredient, exenatide, is a synthetic compound patterned after the exendin-4 hormone that occurs naturally in the saliva of the Gila Monster, a poisonous lizard found in the southwestern United States. (Because of this, some of the fans of the drug call it Gilly or Lizzie.)

Exenatide works by slowing stomach emptying, increasing a feeling of fullness. It also reduces glucagon release from the liver, and may help the cells that produce insulin in the pancreas live longer.

One present downside to Byetta is that it is available only by injection, and has to be taken twice a day. The most common side effect in the studies was nausea, which tended to occur in the initial weeks of taking Byetta but in some cases was so severe it led to withdrawal from the trials.

Even if Byetta remains largely a drug that helps type 2 diabetics with weight loss, there clearly is a huge need since diabetics tend to gain weight on most other medications.

Sanofi-Aventis also clearly is focusing on the huge diabetic market, with four additional clinical trials of Acomplia planned for diabetic and pre-diabetic patients over the next three years.