On April 6, 2026, Amgen announced that its Phase 3 trial of a subcutaneous version of Tepezza (teprotumumab) met its primary endpoint in patients with moderate-to-severe thyroid eye disease. The drug was delivered through an on-body injector (OBI), a small device that patients wear briefly on the skin, and it achieved a 77% proptosis response rate according to Amgen compared to 20% for placebo.
This matters because right now, the only way to get Tepezza is through 8 intravenous infusions at an infusion center, each lasting 60 to 90 minutes, spaced 3 weeks apart over roughly 5 months. For a condition that already disrupts daily life with bulging eyes, double vision, and pain, the treatment itself is a significant burden. A subcutaneous option could change how patients experience therapy.
The Phase 3 OBI Trial Results
The trial enrolled patients with moderate-to-severe active TED diagnosed within the past 15 months. Participants needed at least 3mm of proptosis from their baseline before TED onset. They received either Tepezza or placebo through the on-body injector every 2 weeks for a total of 12 injections over 24 weeks.
Patients were counted as responders if their eye protrusion decreased by 2mm or more at week 24 without the other eye getting worse. The average proptosis reduction was 3.17mm for Tepezza OBI compared to 0.80mm for placebo.
The trial also hit several secondary endpoints: significant improvements in Clinical Activity Score (a measure of disease inflammation), diplopia (double vision) response rates, and quality of life appearance scores. The quality of life visual functioning score showed a numerical trend favoring Tepezza OBI but did not reach statistical significance.
How the OBI Compares to IV Tepezza
Tepezza was originally approved in January 2020 based on a Phase 3 trial data showing an 83% proptosis response rate with IV infusion. The OBI trial showed 77%. That 6-point gap is worth understanding.
The 2 trials used different patient populations and slightly different designs, so a direct comparison is imperfect. What Amgen emphasized in its announcement is that the OBI provides "IV-level efficacy," and the mean proptosis reduction (3.17mm for OBI vs. approximately 3.3mm historically for IV) is comparable. Full results from both trials will be presented at an upcoming medical congress, which should give a clearer picture.
The practical differences between the 2 regimens are significant:
IV Tepezza requires 8 infusions every 3 weeks, each lasting 60 to 90 minutes at an infusion center. Total treatment time: about 8 to 12 hours over 5 months. OBI Tepezza uses 12 injections every 2 weeks, each taking roughly 5 minutes. Total treatment time: under 1 hour over 6 months. The OBI version involves more treatments but far less time per session, and depending on how the FDA structures the approval, some or all injections could potentially happen outside a hospital setting.
Before Tepezza: What Patients Faced
Before January 2020, there was no FDA-approved treatment for thyroid eye disease. Patients with active TED had 2 main options, and neither was great.
The first was high-dose IV corticosteroids, typically methylprednisolone given weekly for 12 weeks. Steroids could reduce inflammation and disease activity but did little for proptosis itself, and they came with substantial side effects: weight gain, blood sugar spikes, insomnia, mood disturbances, and bone thinning with repeated courses.
The second was orbital decompression surgery, where a surgeon removes bone from the eye socket walls to create more space for swollen tissue. This could reduce eye bulging, but it was invasive, irreversible, and only performed after the disease had been inactive for at least 6 months. Many patients also needed follow-up strabismus surgery to correct double vision caused by the decompression itself.
The gap between those 2 options left a lot of patients stuck: too sick for surgery, not helped enough by steroids, and watching their eyes change with no targeted treatment available. Tepezza filled that gap by going after the underlying autoimmune mechanism through IGF-1 receptor inhibition, and the clinical results were dramatic. That said, the drug came with its own set of challenges.
Side Effects: What Patients Need to Know
Tepezza's side effect profile is real and worth understanding before starting treatment. The most common adverse events in the OBI trial (occurring in 10% or more of patients) were muscle spasms, tinnitus (ringing in the ears), weight decrease, ear discomfort, nausea, and diarrhea. These are consistent with what has been reported for IV Tepezza since its approval.
The hearing issue has been the most closely watched safety concern. In the original clinical trials, about 10% of patients reported hearing-related side effects. But real-world observational studies have found much higher numbers. One study of 27 patients found 81.5% reported new auditory symptoms. A study in Endocrine Practice found 16% of 121 patients experienced hearing-related adverse events. According to the FDA's adverse event database, 7.1% of all Tepezza reports between 2020 and 2023 specifically involved hearing loss or impairment.
Based on prospective audiometry studies, the risk of permanent hearing loss appears to be around 3% in patients who had normal hearing before starting treatment. That number is lower than the overall hearing complaint rate because many symptoms (tinnitus, muffled hearing, ear pressure) improve or resolve after treatment ends. Still, for a condition that affects quality of life but is not life-threatening, a 3% chance of lasting hearing damage is something patients should discuss carefully with their doctor.
Other notable side effects include hyperglycemia (high blood sugar), which is relevant for diabetic patients. The drug should not be used during pregnancy due to potential harm to the fetus, and women of childbearing age need effective birth control during treatment and for 6 months after the final dose.
The $27.8 Billion Bet
Tepezza has a complicated business story. Horizon Therapeutics, a small rare disease company, developed and launched it. By 2022, Tepezza was generating nearly $2 billion in annual revenue according to financial reports. That success caught Amgen's attention, and in October 2023, Amgen announced it completed its acquisition of Horizon for $27.8 billion, the largest deal in Amgen's history.
But Amgen inherited a product with stubborn growth limits. Only about 10% of the estimated TED patient population was being treated according to market analysis. Disease awareness among primary care doctors and even some endocrinologists remained low. The IV infusion requirements kept some patients away. Insurance prior authorization for a treatment costing $200,000 to $400,000 per full course could take up to 90 days according to patient reports. And the hearing loss concerns made some physicians hesitant to prescribe.
The OBI formulation is Amgen's answer to at least one of those barriers. By making the drug easier to administer, Amgen is betting that more patients and providers will be willing to start treatment. Whether that translates into the sales growth needed to justify a $27.8 billion purchase price remains to be seen.
What This Means for Patients
Amgen has not announced a regulatory timeline for the OBI formulation. A spokesperson said the company plans to submit the data to regulatory authorities but that approval timing depends on multiple factors. If approved, the subcutaneous version would give TED patients a second option for how they receive treatment.
For patients currently considering Tepezza or already on the IV regimen, the OBI version is not yet available. The IV formulation remains the only approved option. If you are interested in the subcutaneous version, ask your ophthalmologist or endocrinologist about the timeline and whether it might make sense to wait, depending on how urgently your TED needs treatment.
Regardless of how Tepezza is delivered, baseline hearing testing before starting treatment is strongly recommended. The FDA label now advises healthcare providers to assess hearing before, during, and after treatment. If you notice any changes in your hearing, tinnitus, or ear pressure during treatment, report them to your doctor immediately.