Patients may be asking about reports in the lay press that exenatide (Byetta - Med Lett Drugs Ther 2005; 47:45), a synthetic peptide that stimulates release of insulin from pancreatic beta cells, has been used by diabetics and non-diabetics to lose weight. Approved by the FDA to improve glycemic control in patients with type 2 diabetes not controlled by metformin, a sulfonylurea or both, it is given by subcutaneous injection before the morning and evening meals. In clinical trials, some diabetic patients treated with the drug lost weight. No data are available on use in non-diabetics. Exenatide slows gastric emptying and promotes satiety, which is presumably the mechanism of weight loss.

Patients should be warned that exenatide has some adverse effects. Hypoglycemia has occurred when the drug was added to a sulfonylurea but not when it was added to metformin. The risk of hypoglycemia in non-diabetics is unknown. Exenatide often causes nausea, which can be severe, and vomiting. Diarrhea can also occur. Because the drug slows gastric emptying, it can decrease the rate and extent of absorption of other drugs such as antibiotics and oral contraceptives; oral drugs should be taken at least one hour before exenatide.

Perhaps the greatest concern with off-label use of exenatide for weight loss is that 3 times the human dose given to pregnant animals slowed fetal growth and produced skeletal and other developmental abnormalities. The FDA classified it as category C (risk cannot be ruled out) for use during pregnancy. For diabetics and non-diabetics, pregnant or not, exenatide's long-term safety is unknown.