The most common side effect linked to Tepezza treatment is hearing impairment, although some patients taking Tepezza for thyroid eye disease may suffer permanent hearing loss. In one study published in March 2021, researchers found that 65% of patients who took Tepezza experienced some degree of hearing damage or tinnitus, an incidence rate more than six times the rate Horizon reported during Tepezza’s approval process. In another study from February 2022, more than 80% of study participants developed new hearing symptoms after receiving Tepezza infusions. And while most experienced a resolution of their tinnitus, autophony, or ear plugging symptoms after receiving their last Tepezza infusion, less than half of the patients who reported hearing loss/decreased word comprehension reported improvement in their symptoms at 39 weeks post-treatment.

A growing body of research linking Tepezza to hearing function changes and permanent hearing damage has led affected patients to pursue legal claims against Horizon. Plaintiffs in the Tepezza litigation claim, among other things, that Horizon conducted insufficient testing before seeking approval from the FDA for its TED drug, which was based on a clinical trial of only 100 patients. During the FDA review and approval process, Horizon identified hearing damage as a potential side effect of Tepezza but claimed that hearing loss occurred in less than 10% of Tepezza patients and stated that, when it did occur, it was “temporary and generally of limited duration.” However, a growing number of scientific studies and adverse event reports suggest that hearing-related side effects of Tepezza occur more often than previously reported and, in many cases, are permanent.