Tepezza (teprotumumab) works by blocking a specific receptor on cells behind the eyes, stopping the inflammation and tissue expansion that cause the bulging, swelling, and double vision of thyroid eye disease (TED). It is the only FDA-approved treatment for TED and is given as a series of eight intravenous infusions over about six months.
The Receptor Tepezza Targets
In thyroid eye disease, the immune system produces antibodies that mistakenly activate cells called orbital fibroblasts, the connective tissue cells surrounding your eyes. These rogue antibodies don’t just target the thyroid receptor (TSHR) on those cells. They also trigger a second receptor called IGF-1R (insulin-like growth factor 1 receptor), and it turns out the two receptors work together. The thyroid receptor “cross-talks” with IGF-1R, amplifying the signal that tells orbital fibroblasts to produce large amounts of hyaluronic acid, a molecule that attracts water and causes tissue to swell.
Tepezza is a monoclonal antibody that binds directly to IGF-1R and shuts it down. It does not attach to the thyroid receptor at all. Instead, it breaks the crosstalk between the two receptors. Research published in The Journal of Clinical Endocrinology & Metabolism confirmed that when IGF-1R is blocked, the disease-driving antibodies can no longer trigger the receptor partnership responsible for hyaluronic acid overproduction. In lab studies, the drug was effective at very low concentrations, fully inhibiting the disease signal in multiple patient-derived cell lines.
What Changes Behind the Eyes
The practical result of blocking IGF-1R is measurable shrinkage of the tissues pushing the eyes forward. Imaging studies show that Tepezza reduces both the volume of the extraocular muscles (the muscles that move your eyes) and the amount of orbital fat packed into the eye socket. In one study of six patients, every single orbit showed a significant reduction in muscle volume after treatment, to the point that post-treatment measurements were statistically no different from people without thyroid eye disease. Orbital fat volume decreased in 11 out of 12 orbits studied. MRI-based markers of muscle inflammation also dropped significantly.
This tissue reduction is why patients often see improvements in proptosis (how far the eyes protrude), double vision, and the sensation of pressure or pain behind the eyes. The drug addresses the underlying cause of tissue expansion rather than simply dampening general inflammation the way steroids do.
The Infusion Schedule
Tepezza is given through an IV, not taken as a pill. The standard regimen is eight infusions spaced three weeks apart, meaning the full course runs roughly 21 weeks (about five months). The first infusion uses a lower dose of 10 mg per kilogram of body weight. The remaining seven infusions each use 20 mg/kg. Each session takes place at an infusion center, and the drug is approved for thyroid eye disease regardless of whether the disease is currently active or has become chronic.
Blood Sugar Effects
Because IGF-1R plays a role in how the body processes insulin, Tepezza can raise blood sugar, sometimes significantly. In a study of 42 patients, 52% experienced some degree of hyperglycemia during treatment. The risk depended heavily on baseline metabolic health:
- Normal blood sugar at baseline: 41% developed hyperglycemia
- Prediabetes at baseline: 30% developed hyperglycemia
- Existing diabetes at baseline: 100% experienced worsened blood sugar control
Most cases were mild or moderate, but one patient in the study experienced a life-threatening blood sugar spike. The hyperglycemia typically appears within the first 12 weeks of treatment. If you have diabetes, your blood sugar will almost certainly need closer monitoring and possible medication adjustments throughout the infusion course. For everyone, blood glucose is typically checked before each infusion, and screening with a fasting glucose and HbA1c is recommended before starting treatment.
Hearing Changes
Hearing loss is the other notable side effect. The original clinical trial reported subjective hearing problems in about 10% of patients and described them as reversible. However, that finding was based on patient reports, not formal hearing tests. Later research using actual audiometric testing found otological side effects in up to 30% of patients, and some cases turned out to be chronic rather than temporary.
Audiologists and researchers now recommend baseline hearing tests before the first infusion, ideally with repeat testing after each session and again after the full course is complete. At a minimum, hearing should be formally assessed before, during, and after treatment. If you notice muffled hearing, ringing in the ears, or a sense of fullness in one or both ears during treatment, flagging it early gives your care team the most options.
Why It Differs From Older Treatments
Before Tepezza, the main options for thyroid eye disease were corticosteroids to reduce inflammation, orbital radiation, and surgery to decompress the eye socket or correct misaligned muscles. Steroids suppress the immune response broadly but don’t reverse the tissue buildup already present, and symptoms often return once steroids are stopped. Surgery addresses the physical consequences of the disease but not the molecular process driving it.
Tepezza works upstream of all that. By targeting the specific receptor crosstalk responsible for tissue expansion, it can shrink muscle and fat volumes back toward normal rather than simply slowing further damage. This is why imaging studies show post-treatment eye socket anatomy that resembles healthy controls, something steroids and radiation rarely achieve. That said, the infusion course is expensive, carries the metabolic and hearing risks described above, and some patients do experience disease recurrence after completing treatment, potentially requiring retreatment.