Study Finds Similar Cardiovascular Results for Generic and Branded Medications for Hypothyroidism


JACKSONVILLE, Fla. – A new study by Mayo Clinic researchers may have broad implications for the treatment of patients with predominantly benign thyroid disease and newly treated hypothyroidism.

The study, to be published in Proceedings of the Mayo Clinic in July, analyzed whether generic and brand-name levothyroxine therapy affected hospitalization for cardiovascular events in those patients at increased risk of coronary heart disease and heart failure. Levothyroxine is the most prescribed medicine in the US, with more than 23 million prescriptions written annually.

Retrospective analysis, using data from identified claims from a large US private health plan, found that cardiovascular event rates were similar for generic and brand name levothyroxine therapy with lower pharmacy costs for the generic drug. The results, if confirmed by research on long-term event rates, suggest that generic or brand-name levothyroxine can be used to treat hypothyroidism due to benign thyroid disorders. The average 30-day cost of the generic drug was about half the cost of brand-name drugs for patients and insurers.

"More than 90% of thyroid prescriptions are for levothyroxine, and there has been disagreement over whether the generic levothyroxine and thyroxine brand preparations are equivalent," says Robert Smallridge, MD, an endocrinologist at Mayo Clinic and the study's lead investigator. "These findings suggest that generic and brand-name levothyroxine therapy is similar to that related to the risk of cardiovascular events."

Dr. Smallridge says the results require confirmation with long-term follow-up and study of subgroups of patients, such as those with a history of thyroid cancer, who frequently receive higher doses of levothyroxine.

Hypothyroidism, or hypoactivity of the thyroid gland, affects the function of many body organs, raising blood cholesterol levels and increasing the risk of heart attacks, heart failure and stroke. Levothyroxine is used to reduce high cholesterol and reverse the symptoms of hypothyroidism. US brands for levothyroxine include Levothroid, Levoxyl, Synthroid, Tirosint and Unithroid.

The analysis was unusual because it used information from an administrative request database provided by the OptumLabs Data Warehouse. OptumLabs was co-founded by Optum Inc. and Mayo Clinic in 2012. This data warehouse contains data from identified administrative claims as well as electronic health record data from a national network of provider groups.

The study reviewed records of 87,902 patients followed up for an average of one year, focusing on hospitalization for heart attacks, congestive heart failure, atrial fibrillation, or strokes. The analysis found no difference in event rates for the four types of cardiovascular events.


Dr. Smallridge is the Alfred D. and Audrey M. Petersen Professor of Cancer Research and deputy director of the Mayo Clinic Cancer Center in Jacksonville. The study was funded by Robert D. and Patricia E. Kern Center of the Mayo Clinic for Health Care Science, with an additional gift from Alfred D. and Audrey M. Petersen.

About Proceedings of the Mayo Clinic

Proceedings of the Mayo Clinic is a peer-reviewed medical journal that publishes original articles and reviews on clinical and laboratory medicine, clinical research, basic science research, and clinical epidemiology. Proceedings is sponsored by the Mayo Foundation of Medical Education and Research as part of its commitment to medical education. Publishes submissions from authors around the world. The magazine is published over 80 years and has a circulation of 130,000. Visit the Proceedings of the Mayo Clinic website to view articles.

About Mayo Clinic

The Mayo Clinic is a non-profit organization committed to clinical practice, education and research, providing specialized and comprehensive care to all who need healing. Learn more about Mayo Clinic. Visit the Mayo Clinic News Network.

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