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Eli Lilly is making tirzepatide, branded as Zepbound for weight loss, available in vials for patients who pay out-of-pocket.

(CNN) — Starter doses of the weight-loss drug Zepbound are now available in single-dose vials, drug manufacturer Eli Lilly announced Tuesday, a move the company says will “significantly” expand supply as it sees continued high demand.

Instead of a preloaded injector pen, patients will use a syringe to draw out the medicine.

Tirzepatide, the active ingredient in Zepbound and Mounjaro, is part of new class of medications used to treat obesity and diabetes that have skyrocketed in popularity, driving shortages — and leading some people to use versions made by compounding pharmacies.

“These new vials not only help us meet the high demand for our obesity medicine, but also broaden access for patients seeking a safe and effective treatment option,” Patrik Jonsson, president of Lilly Cardiometabolic Health and Lilly USA, said in a statement.

The new vials will be available exclusively to people who pay out of pocket through LillyDirect, a company platform that helps coordinate telehealth services and fill prescriptions for patients.

A four-week supply of 2.5-milligram (mg) vials is $399, and a four-week supply of 5-mg vials is $529, less than half the list price of other GLP-1 medicines for obesity, according to Eli Lilly.

These prices are in line with those offered through Lilly’s savings program for uninsured people, the company said. But the option to pay out-of-pocket for the vials now expands access to patients who aren’t eligible for the savings program, such as those on Medicare.

“Despite obesity being recognized as a serious chronic illness with long-term consequences, it’s often misclassified as a lifestyle choice, resulting in many employers and the federal government excluding medications like Zepbound from insurance coverage,” Jonsson said. “Outdated policies and lack of coverage for obesity medications create an urgent need for more innovative solutions. Bringing Zepbound single-dose vials to patients will help more people living with obesity manage this chronic condition. We will also continue to advocate for a system that better aligns with the science.”

Tirzepatide works by mimicking hormones that stimulate the release of insulin, increase feelings of fullness and reduce appetite. It targets two hormone receptors, GIP and GLP-1. Semgalutide, known as Ozempic for diabetes and Wegovy for weight loss, is also part of this broad class of drugs.

The ongoing shortages of tirzepatide and other popular weight-loss drugs have allowed for compounded versions of the treatments – with similar or related ingredients – to hit the market, with less oversight and regulation from the US Food and Drug Administration.

The FDA has issued a warning last month about compounded versions of semaglutide; the agency says that it has received reports of adverse events – some requiring hospitalization – due to dosing errors related to units of measurement, varying product concentrations and use of multiple-dose vials. Patients “should not use a compounded drug if an approved drug is available,” the agency has said.

Eli Lilly has also raised concerns about the potential risks that compounded versions of its drugs pose to patients. In an open letter in June, the company emphasized that it is the “only lawful supplier of FDA-approved tirzepatide medicines” and that products from other unverified sources may be “fake, counterfeit, or otherwise unsafe products.”

“[Safety] is our number one priority, and this is a great way for patients to know they’re getting genuine Lilly medicine,” said Rhonda Pacheco, group vice president for Lilly US Cardiometabolic Health. Thousands of people use LillyDirect each week, she said.

The experience for people who self-inject tirzepatide with a syringe that was filled from a vial would probably be similar to using a prefilled pen — and it might come with some added benefits, said Dr. Jody Dushay, an endocrinologist at Beth Israel Deaconess Medical Center and assistant professor of medicine at Harvard Medical School.

“It’s old school, but I have patients with type 1 and 2 diabetes who prefer vial and syringe to pen devices. I don’t think it is a much bigger deal to use an insulin syringe vs auto injector, unless someone has severe needle phobia,” she wrote in an email. “It’s not that difficult to draw up a syringe, although the elderly, those with limited dexterity, and those with poor vision will be better off with the auto injector.”

The syringe and vial might actually allow for some added flexibility in doses, especially for starting levels, Dushay said. Patients could draw up less than 2.5 mg if they’re having severe side effects or less than 5 mg if they’re ready to increase but not quite double the dose.

Also, most compounded versions of tirzepatide come in vials, so patients should be especially careful with the source of their medication, she noted.

Clinical trial data found that people using 5-mg injections of tirzepatide lost about 15% of their weight after more than a year of treatment, on average.

Another recent study found that people using tirzepatide injections lost more weight and were more likely to reach specific weight loss targets than those on semaglutide.