How long people stay on GLP-1 medicines: a US insurance study

Why this study matters

In clinical trials of GLP-1 medicines, the abstract notes that more than 85% of participants keep taking the medicine. Outside trials, people face costs, supply problems, side effects and the everyday effort of weekly or daily injections. This study used real prescription and medical claims from a large US insurer to measure how many people kept going. For Canadian readers, it offers a picture of real-world use in a system with different coverage rules from ours, and a reminder that trial results assume people stay on treatment.

Who was in the study

The study drew on integrated pharmacy and medical claims from an average of 16.5 million commercially insured people per month. It identified adults aged 19 or older with obesity and without diabetes who newly started a GLP-1 medicine between January 1 and December 31, 2021. People had to be continuously enrolled with the insurer for one year before and one year after starting. 4,066 people met all criteria. The mean age was 46 years and 81% were women. The summary we reviewed does not report which specific GLP-1 medicines each person started or at what dose.

What the researchers did

This was a retrospective cohort study. Retrospective means the researchers looked back at existing records. Cohort means a defined group was tracked over time. No treatment was assigned; the study simply describes what happened.

Persistence was defined as continuing to fill prescriptions with no gap of 60 days or more, and switching between GLP-1 products was allowed without counting as stopping. Adherence was measured as the proportion of days covered (PDC), the share of days in the year on which the person had medicine available according to their refills. People with a PDC of 80% or more were counted as adherent. Switching between GLP-1 products was also described.

What they found

At 180 days, 46.3% of people were still persistent. At one year, 32.3% were (R32-C132). In other words, about a third met the study's definition of staying on treatment for a full year.

The average proportion of days covered was 51.0%, and 27.2% of people were adherent. 11.1% switched from one GLP-1 product to another during the year.

The abstract also reports persistence figures for individual products. We do not list them here, because the study was not designed to compare medicines and the products available in 2021 differed from those available now. The authors describe one-year persistence and adherence overall as poor, and switching as low.

Side effects and people who stopped

Claims data do not record why prescriptions stopped. This study did not measure side effects. The published summary we reviewed does not report a discontinuation rate, and the extracted data specifically caution against calculating one as 100 minus the persistence figure, because persistence and discontinuation are defined differently.

What this study does not tell you

• The study cannot say why people stopped. Cost, insurance rules, supply shortages, side effects and reaching a personal goal are all possible reasons that claims data cannot separate.
• Everyone started treatment in 2021. Which products were available, and how they were covered, has changed since, so the numbers may not reflect current patterns.
• Everyone had continuous commercial insurance for two years. People who lost coverage, changed jobs, or had public insurance were excluded.
• Filling a prescription is not the same as taking the medicine.
• Product-level figures in this study are descriptive and do not show that one medicine is easier to stay on than another.
• The results come from the US system. Canadian coverage, prices and prescribing differ.
• The summary we reviewed does not state the funding source.

What it means in Canada

This study shows that in one US insured population, most people did not stay on a GLP-1 medicine for a full year by the study's definition. It does not tell any Canadian reader what to expect personally, and it does not say whether any medicine is right for anyone. Coverage rules can strongly affect whether people keep filling prescriptions; see public drug coverage by province. For information about specific medicines, see semaglutide in Canada and liraglutide in Canada. To see how support programs differ, see compare services.

Related reading

Other studies in this library that bear on the same question.

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