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

Felbamate is one of the most effective antiepileptic drugs available for certain severe, treatment-resistant seizure disorders—but it also carries the most serious safety warnings of any approved anticonvulsant. Before taking felbamate, your neurologist is required to review its risks with you and obtain your written consent. Understanding exactly what those risks are, what common side effects to expect, and what symptoms demand immediate medical attention is critical to staying safe while on this medication.

The Black Box Warnings: What They Mean

Felbamate carries two black box warnings—the FDA's most serious level of warning. These are not theoretical risks; they are based on real patient outcomes identified after the drug entered widespread use in 1993.

1. Aplastic Anemia

Aplastic anemia is a life-threatening condition in which the bone marrow stops producing enough blood cells—red blood cells, white blood cells, and platelets. Patients on felbamate face a risk of aplastic anemia estimated to be more than 100 times greater than the general population (approximately 27–207 cases per million patient-years, compared to 2–2.5 per million in the general population). The case fatality rate ranges from 20–30%, and higher rates have been reported.

Key facts about felbamate and aplastic anemia:

Most cases occurred in the first 5–30 weeks after starting felbamate, but risk persists beyond this window

Among 34 reported cases in the first 6 years after approval, none occurred in children under age 13; most patients were adults over 17

There is no known way to predict or prevent aplastic anemia from occurring; routine CBC monitoring can detect early changes but cannot guarantee prevention

Patients with a personal or family history of blood dyscrasia are contraindicated from using felbamate

Warning Signs of Aplastic Anemia — Call Your Doctor Immediately:

Fever, chills, or repeated infections that don't resolve

Unusual bleeding or bruising; nosebleeds; bleeding gums

Red or purple spots on the skin (petechiae)

Unusual tiredness, weakness, or shortness of breath

Sores, ulcers, or white spots in the mouth

2. Hepatic (Liver) Failure

Acute liver failure is the second black box warning. The reported rate in the U.S. is approximately 6 cases of liver failure per 75,000 patient-years of felbamate use. Of reported cases, approximately 67% resulted in death or liver transplantation—usually within 5 weeks of the onset of symptoms. Felbamate is absolutely contraindicated in patients with any history of hepatic dysfunction.

Warning Signs of Liver Failure — Seek Care Immediately:

Yellowing of the skin or whites of the eyes (jaundice)

Dark urine or pale, clay-colored stools

Pain or tenderness in the upper right abdomen

Persistent nausea, vomiting, or loss of appetite

Unusual fatigue or weakness

Common Side Effects of Felbamate

Beyond the black box warnings, felbamate causes a range of common side effects that affect many patients. These are generally manageable and often improve as your body adjusts to the medication or with dose adjustment.

In adults taking felbamate as monotherapy, the most common side effects are:

Anorexia (loss of appetite) and weight loss

Nausea and vomiting

Insomnia and sleep disturbances

Headache

Dizziness

Somnolence (drowsiness)

Double vision (diplopia)

Changes in taste perception

Gait disturbance (trouble with balance and coordination)

Suicidal Thoughts: A Warning for All AEDs

Felbamate, like all antiepileptic drugs, carries an FDA warning about an increased risk of suicidal thoughts and behaviors. This is a class-wide warning that applies to all antiseizure medications. Patients, family members, and caregivers should monitor for new or worsening depression, unusual mood changes, or any signs of suicidal ideation and contact their healthcare provider immediately if these occur.

Tips for Managing Common Side Effects

Nausea: Take felbamate with food unless your doctor has told you otherwise. Small, frequent meals may help.

Insomnia: Avoid doses close to bedtime if possible; discuss timing adjustments with your neurologist.

Dizziness or drowsiness: Do not drive or operate heavy machinery until you know how felbamate affects you. This is especially important when starting the medication or after dose increases.

Weight loss: Monitor your weight and report significant loss to your neurologist. A dietitian referral may be appropriate for children on felbamate.

Some side effects of felbamate are made worse by drug interactions. See our article on felbamate drug interactions: what to avoid for a detailed review of how other medications can change felbamate's effects and vice versa.