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

Megestrol acetate (brand name Megace, Megace ES) is a progestin medication used to stimulate appetite and treat certain cancers. Like all medications, it can cause side effects — some expected and manageable, others serious enough to require immediate medical attention. Here's a comprehensive guide to what to expect.

Common Side Effects of Megestrol

The following side effects are seen frequently in patients taking Megestrol, especially at the high doses used for appetite stimulation (400-800 mg/day):

Weight gain (15-70%): This is actually a desired therapeutic effect for most patients — Megestrol significantly increases appetite and promotes weight gain. The weight gained is predominantly fat mass, not lean muscle.

Nausea (7%): Some patients experience nausea early in treatment; this often improves as the body adjusts. Taking Megestrol with food may help.

Edema (5%): Fluid retention can cause swelling in the hands, feet, or legs. Report significant or sudden swelling to your doctor.

Vaginal bleeding (7-8%): Breakthrough bleeding can occur in women taking Megestrol due to its progestogenic activity. Report any unexpected vaginal bleeding to your prescriber.

Impotence / decreased libido: Megestrol suppresses sex hormone levels (testosterone in men, estrogen/progesterone in women), causing sexual dysfunction in many patients. This is typically reversible after stopping the medication.

Hypertension: Blood pressure elevation has been reported. Monitor blood pressure regularly while on Megestrol, especially if you already have hypertension.

Diarrhea and flatulence: GI symptoms were reported in >5% of patients in clinical trials for the oral suspension formulation.

Rash and skin changes: Reported in some patients. Mild rashes usually resolve on their own; severe or widespread skin reactions should be reported to your doctor.

Serious Side Effects — Call Your Doctor

The following side effects are less common but can be severe. Contact your healthcare provider promptly if you experience any of these:

Adrenal insufficiency: Long-term Megestrol use suppresses the adrenal glands. Stopping suddenly — especially in a stressed state (illness, surgery) — can cause adrenal crisis. Symptoms: severe dizziness, low blood pressure, profound fatigue, nausea, vomiting. This is a medical emergency.

Cushing's syndrome: Chronic high-dose use can produce Cushing's syndrome-like symptoms: moon face (rounded, puffy face), central obesity, easy bruising, stretch marks, muscle weakness, high blood sugar. Report these symptoms to your doctor.

Blood clots (thromboembolic events): Megestrol can increase the risk of deep vein thrombosis (DVT) and pulmonary embolism (PE). Symptoms of DVT: leg pain, swelling, redness. Symptoms of PE: sudden shortness of breath, chest pain, coughing blood. Call 911 or go to the ER immediately if you experience these.

New or worsening diabetes: Megestrol can raise blood sugar levels. Patients with pre-existing diabetes or risk factors should monitor blood glucose closely. Symptoms of high blood sugar: increased thirst, frequent urination, blurred vision, fatigue.

Hypogonadism: Prolonged use suppresses sex hormone production. In men, this can cause significantly low testosterone, with symptoms of fatigue, muscle loss, depression, and osteoporosis. Discuss monitoring with your doctor.

Pregnancy Warning — Do Not Take If Pregnant

Megestrol is contraindicated in pregnancy. Animal studies show it causes fetal harm, including reduced fetal weight and feminization of male fetuses. A negative pregnancy test is required before starting Megestrol, and effective contraception must be used during treatment. If you become pregnant while taking Megestrol, contact your doctor immediately.

What to Watch For: A Quick Summary

Call 911/ER immediately: chest pain, sudden shortness of breath, coughing blood, severe dizziness/collapse

Call your doctor soon: leg swelling/pain, unexpected vaginal bleeding, moon face, blood sugar changes, new symptoms after stopping Megestrol

Monitor and mention at next visit: weight changes, blood pressure, sexual side effects, swelling, GI symptoms

Also important to know: Megestrol Drug Interactions: What to Avoid and What to Tell Your Doctor.

If side effects are making you consider stopping Megestrol, always discuss with your doctor first. And if you're having trouble finding Megestrol at your pharmacy, medfinder can help locate pharmacies with it in stock near you.