Ogsiveo Side Effects: What to Expect and When to Call Your Doctor

Starting Ogsiveo (nirogacestat) means starting an effective treatment for your desmoid tumor — and it also means knowing what side effects to expect. The good news is that most Ogsiveo side effects are manageable with supportive care and dose adjustments. The key is knowing which symptoms are expected versus which ones require prompt medical attention.

This guide covers the full range of Ogsiveo side effects — from common and mild to serious and rare — along with practical management tips based on the drug's clinical trial data and prescribing information.

Most Common Ogsiveo Side Effects (Occurring in ≥15% of Patients)

In the Phase 3 DeFi clinical trial, these side effects occurred in at least 15% of patients taking Ogsiveo:

Diarrhea (84%): This is the most common side effect. Diarrhea can be severe — Grade 3-4 events occurred in 16% of patients. Stay hydrated, use antidiarrheal medications like loperamide (Imodium) as directed, and call your doctor if diarrhea lasts more than 3 days or is accompanied by fever or severe pain.

Ovarian toxicity (75% in women of reproductive potential): This manifests as irregular periods, missed periods, hot flashes, night sweats, or vaginal dryness — signs of reduced ovarian function. Notably, 74% of affected women had recovery of ovarian function during or after treatment. Report any changes in your menstrual cycle to your doctor promptly.

Rash (68%): Skin rash is common. Tell your care team about any new skin changes, including rashes, as this can sometimes require dose adjustment. Separately, Ogsiveo may increase the risk of non-melanoma skin cancers (squamous cell carcinoma: 2.9%; basal cell carcinoma: 1.4%).

Nausea (54%): Nausea is common but usually manageable. If you vomit after taking a dose, do not retake it — wait until your next scheduled dose time. Anti-nausea medications prescribed by your doctor can help.

Fatigue (54%): Feeling tired is very common with Ogsiveo. Conserve your energy for activities that matter most. Report extreme or debilitating fatigue to your doctor.

Stomatitis / mouth sores (39%): Inflammation and sores in the mouth can affect eating and speaking. Gentle oral care, soft foods, and prescription mouth rinses can help. Tell your care team about any mouth pain.

Headache (30%), abdominal pain (22%), cough (20%), hair loss (19%), upper respiratory infection (17%), shortness of breath (16%): These are less frequent but still commonly reported. Most are manageable with supportive care.

Serious Side Effects That Require Immediate Attention

The following side effects are serious and require prompt contact with your healthcare provider:

Liver problems (hepatotoxicity): ALT elevations occurred in 30% and AST elevations in 33% of patients. Symptoms of liver damage include nausea, upper right stomach pain, yellowing of the skin or eyes (jaundice), dark urine, or light-colored stools. Regular blood tests will monitor your liver function.

Electrolyte abnormalities: Low phosphate (hypophosphatemia) and low potassium (hypokalemia) can occur. Symptoms include muscle weakness, muscle pain, abnormal heart rate, or confusion. Blood tests will track your electrolyte levels.

Non-melanoma skin cancer: Your doctor should examine your skin before and during treatment. Report any new skin growths, changes to existing spots, or non-healing sores.

Embryo-fetal toxicity: Ogsiveo can cause serious fetal harm. If you are pregnant or become pregnant while taking Ogsiveo, contact your doctor immediately. Effective contraception is required during treatment and for 1 week after your last dose.

Important Monitoring Schedule

While you're on Ogsiveo, your care team will monitor you with regular blood tests and clinical assessments. Do not skip these appointments — many serious side effects are caught early through lab work before symptoms appear. Typical monitoring includes:

Liver function tests (ALT, AST) — regularly throughout treatment

Electrolytes (potassium, phosphate) — regularly throughout treatment

Skin examination — before starting and periodically during treatment

Menstrual cycle monitoring for women of reproductive potential

Pregnancy test — required before starting treatment

When to Call Your Doctor Right Away

Contact your healthcare provider immediately if you experience any of the following:

Diarrhea lasting more than 3 days despite antidiarrheal medications

Severe abdominal pain or fever with diarrhea

Yellowing of skin or eyes, dark urine, or severe fatigue (liver symptoms)

Significant changes in menstrual cycle or sudden onset of menopause symptoms

New skin growths, ulcers, or changes to existing spots

Muscle weakness, abnormal heartbeat, or confusion (electrolyte symptoms)

Positive or suspected pregnancy

For more on how Ogsiveo interacts with other medications, see our guide on Ogsiveo drug interactions. For a broader overview of the medication, see what is Ogsiveo and how does it work.