STORY: An analysis provided to Reuters exclusively showed that the popular weight loss drugs Wegovy and Ozempic have seen a steady decline in use over time.

The analysis of U.S. pharmacy data showed that only one in four Americans prescribed Wegovy or Ozempic for weight loss were still taking it two years later.

The analysis does not include details about why patients quit using the medications.

But the decline in use is spurring a debate over the drugs' cost to patients, employers and government health plans.

Novo Nordisk's Wegovy or Ozempic can cost more than $1,000 per month, and may require extended use to see meaningful benefits.

The price tag has drawn fire recently from President Joe Biden and other public officials, who said such drugs could cost the country $411 billion per year... and that's if only half of adults with obesity used them.

Drug manufacturers have been unable to keep up with unprecedented demand for the new weight loss drugs.

In response to the analysis, Novo Nordisk said it (quote) "does not believe these data are sufficient to draw conclusions about overall patient adherence and persistence to various GLP-1 medicines, including our treatments."

A co-author of the analysis said the reason patients may stop their prescriptions was likely a mix of side effects, out-of-pocket costs and supply shortages.

Doctors said some patients may decide to stop the medication after successfully losing weight. Other studies have shown that most patients who stop using the drugs usually regain most of the weight.