The National Community Pharmacists Association is supporting the letter-writing campaign and asking its members to participate.

The history: Drugmakers originally began selling drugs based on semaglutide and tirzepatide to help people with diabetes control their blood pressure. Since then, studies have shown that patients can use the drugs to lose weight.

Other studies are showing that the drugs may help people control conditions such as liver disease, kidney disease, cancer and even Alzheimer's disease.

But the brand-name versions of the drugs aimed at people fighting obesity often cost more than $1,000 per month per patient.

The versions created by the compounding pharmacies often cost less than $250 per month.

About half of employers surveyed by WTW said they were interested in using compounded GLP-1 agonists to reduce the cost of helping employees fight obesity.

Related: Employers turn to alternative strategies to control health care spending

Executives from Eli Lilly, the maker of tirzepatide, the main active ingredient in Zepbound, have suggested that the tirzepatide substitutes created by compounding pharmacies are often full of impurities and sometimes contaminated by bacteria.

Compounding policy: The GLP-1 agonist compounding fight has put a spotlight on the FDA rules governing compounding pharmacies.

The New Jersey attorney general's office summarized the issues in a statement on a semaglutide compounding based on the views of the New Jersey Board of Pharmacy.

Federal law normally prohibits pharmacies from compounding drugs that are "essentially copies of a commercial available drug product," but they can compound drugs like GLP-1 agonists that are on the FDA's list of drugs affected by shortages, according to the statement.

One concern is that getting a suitable semaglutide base is difficult, in part because it's not yet clear whether the "salt form" of the drug has the same effects as the base, and in part because compounders are not supposed to use a semaglutide base that's labeled as being created for research purposes only or as being not fit for human use, the board said.

The FDA itself has expressed concerns about the possibility that some products that seem to be versions of GLP-1 agonists may be poorly compounded, may have unclear origins or may contain the wrong ingredients.

The FDA "has received reports of adverse events related to compounded versions of semaglutide and tirzepatide," the FDA says in a notice posted in October. "However, federal law does not require state-licensed pharmacies that are not outsourcing facilities to submit adverse events to FDA, so it is likely that adverse events from compounded versions of these drugs are underreported."

What it means: For employers, benefits brokers and benefits consultants, the compounding fight might be a reason to go slow on providing routine coverage for any compounded or brand-name GLP-1 agonists for weight loss.

The FDA itself says in the October notice that the adverse event reports associated with use of compounded GLP-1 agonist products seem to be similar to the adverse event reports related to use of the brand-name versions of the drugs.

"It is not always possible to determine if the adverse event directly resulted from use of the drug or if other factors may have contributed to these adverse events," the FDA says.

But employers may wonder why they should risk paying even $2,400 per year, let alone $12,000 per year, to cause otherwise healthy employees who are fighting obesity to suffer from adverse events.

A Maine resident is seeking class-action status for a suit over an employer-sponsored health plan's failure to pay for GLP-1 agonist prescriptions.

But law firms are also trying to organize class-action suits over conditions such as blood clots and vision loss that have affected some people taking GLP-1 agonists.