By Amara Osei

Forty-four percent of U.S. adults taking GLP-1 weight-loss medications such as Wegovy and Zepbound changed how they take the drugs from the way they were prescribed, according to a Centers for Disease Control and Prevention report released on Thursday. The finding sets the baseline for the pricing and access decisions now facing Eli Lilly, Novo Nordisk and the Medicare program.

What did the CDC measure?

The CDC's Rapid Surveys System, a fast-turnaround polling instrument built to track emerging health behaviours, collected responses from 8,118 U.S. adults in July and August 2025. An estimated 9.8% of adults said they had used a GLP-1 drug at some point over the previous year. Of those users, 976 in the sample received follow-up questions about how they use the medication.

The modifications broke down as follows:

• Skipped doses: 28% of users
• Cost cited as the reason for a change: 38% of users who changed
• Availability cited as the reason for a change: 36% of users who changed
• Reduced or stopped the drug because of side effects or symptoms: about 12% of users

Cost and availability together account for nearly three-quarters of the stated reasons among changers, a concentration that points to price and supply rather than tolerability as the dominant friction.

How does age split the modifications?

Modification rates ran highest among the youngest users: 54% of those aged 18 to 39 changed their use, compared with 30% of users 65 and older. Among younger users who made changes, 58% cited cost, against 20% of older users. That 38-point gap identifies price as the primary pressure point for working-age adults, while delayed prescription fills — reported by 37% of the younger group against 6% of the older group — show where the substitution occurs.

Why do compounded versions matter?

Compounded formulations, prepared by a pharmacy rather than the original manufacturer, were used by 22.6% of GLP-1 users, and another 8.8% could not say whether their product was compounded. The Food and Drug Administration, the federal agency that reviews and approves medicines, does not vet compounded GLP-1 medications for safety, effectiveness or manufacturing quality before they reach the market. Modification rates reached 62% among compounded-drug users, against 36% among users of other formulations.

What does the evidence support?

About 12% of users reported reducing or stopping their medication because of side effects or symptoms. The CDC said more evidence on the safety and effectiveness of these real-world practices could help guide clinical guidelines. The report documents the scale of departure from prescribed regimens, and it does so alongside a candid list of limits: the two survey panels posted cumulative response rates of 13.3% and 3.8%, and the findings rely on self-reported answers. The 44% figure therefore carries the weight of an estimate rather than a census.

What does it mean for Lilly, Novo and Medicare?

The fieldwork predates the latest industry response. Before the survey closed in August 2025, Eli Lilly and Novo Nordisk intensified their push to make the drugs easier to obtain and to take in lower-priced compounded versions, according to Bloomberg. Federal action to broaden access has also moved forward, with Medicare patients among those now covered.

Price has been the binding constraint throughout. FDA-approved weight-loss drugs carry a sticker price that can top $1,000 a month without insurance or discounts, which helped drive demand for compounded versions during shortages of approved product. Since July 1, the Medicare GLP-1 Bridge program offers eligible beneficiaries weight-loss drugs for $50 a month, against branded sticker prices that can exceed $1,000. The 44% modification rate, measured before the compounded push and the $50 program reached full traction, gives both companies and policymakers the figure they will measure the next phase against.