What Is Ogsiveo? Uses, Dosage, and What You Need to Know in 2026

Ogsiveo (nirogacestat) is a prescription medication that represents a significant milestone in cancer medicine: it is the first and only FDA-approved treatment specifically developed for desmoid tumors. Before its approval on November 27, 2023, there was no systemic therapy with FDA approval for this rare and often painful condition. Here's everything you need to know about what Ogsiveo is, what it treats, how it's taken, and what results patients can expect.

What Is Ogsiveo (Nirogacestat)?

Ogsiveo is the brand name for nirogacestat, a selective gamma secretase inhibitor (GSI). It was developed by SpringWorks Therapeutics, which became a wholly owned subsidiary of Merck KGaA in July 2025. The drug is classified as an antineoplastic agent — meaning it is designed to suppress tumor growth.

Ogsiveo comes as an oral tablet — you take it by mouth twice a day. It does not work by attacking fast-dividing cells the way traditional chemotherapy does. Instead, it targets a specific enzyme pathway that is responsible for driving desmoid tumor growth.

What Is Ogsiveo Used For?

Ogsiveo is FDA-approved for adults with progressing desmoid tumors who require systemic treatment (treatment by mouth or injection). This is the only currently approved indication.

Desmoid tumors are rare, non-cancerous but locally aggressive tumors that arise from connective tissue (the tissue that holds muscles, tendons, and ligaments together). Although they don't spread to other parts of the body like malignant cancers, desmoid tumors can:

Grow aggressively and invade nearby structures

Cause severe pain, restricted movement, and functional impairment

Compress nearby organs or blood vessels

Recur after surgery, making surgical treatment less reliable

Ogsiveo is indicated for patients whose tumors are actively progressing — meaning they are growing or causing significant symptoms — and who need systemic (whole-body) treatment. It is not indicated for all desmoid tumor patients; some may be candidates for active surveillance or other treatment modalities.

How Effective Is Ogsiveo?

Ogsiveo's approval was based on the Phase 3 DeFi trial, which is the largest completed clinical trial of an FDA-approved treatment for adult desmoid tumor patients. Key results:

41% objective response rate (tumor shrinkage) with Ogsiveo vs 8% with placebo

7% complete response rate (tumor disappeared completely) with Ogsiveo vs 0% with placebo

76% of patients remained progression-free at 2 years with Ogsiveo vs 44% with placebo

71% reduction in risk of disease progression or death compared to placebo

Patients also reported meaningful improvements in pain, physical function, and overall quality of life. Responses typically began appearing around 5 to 6 months into treatment.

What Is the Ogsiveo Dosage?

The standard recommended dose of Ogsiveo is 150 mg taken orally twice daily — morning and evening. Treatment continues until disease progression or unacceptable toxicity.

Important dosing rules:

Can be taken with or without food

Swallow tablets whole — do not crush, chew, or break

If you vomit after a dose, do not retake it — wait for your next scheduled dose

If you miss a dose, take the next dose at its regular time — do not double up

Avoid grapefruit, Seville oranges, and starfruit — these can increase drug levels

If using antacids, take Ogsiveo at least 2 hours before or after; avoid PPIs and H2 blockers if possible

If you experience significant side effects, your doctor may reduce your dose to 100 mg twice daily or temporarily pause treatment.

Is Ogsiveo a Chemotherapy Drug?

No. Ogsiveo is not chemotherapy. Traditional chemotherapy targets all rapidly dividing cells — including healthy cells — which causes the classic side effects people associate with cancer treatment (hair loss, nausea, immune suppression). Ogsiveo is a targeted therapy that specifically blocks the gamma secretase enzyme, which plays a key role in Notch signaling — a pathway that drives desmoid tumor growth. This means it works through a very different mechanism.

Who Is Ogsiveo Approved For?

Ogsiveo is approved for adults (18 years and older) with desmoid tumors that are actively progressing and require systemic treatment. It has not been studied or approved in children or adolescents. It is not currently approved for multiple myeloma, ovarian cancer, or other tumor types — though trials are underway to evaluate it in those settings.

To learn more about how Ogsiveo works at the molecular level, see our article on Ogsiveo's mechanism of action. For what to expect in terms of side effects, see our comprehensive guide on Ogsiveo side effects.