What are the possible side effects of FIRDAPSE?

FIRDAPSE may cause serious side effects, including:


  • You could have a seizure even if you never had a seizure before.
  • Do not take FIRDAPSE if you have ever had a seizure.
  • Stop taking FIRDAPSE and call your doctor right away if you have a seizure while taking FIRDAPSE.
  • See more information about seizures here

See “What is the most important information I should know about FIRDAPSE?” in FIRDAPSE Prescribing Information.

Serious allergic reactions, such as anaphylaxis. FIRDAPSE can cause serious allergic reactions. Stop taking FIRDAPSE and call your doctor right away or get emergency medical help if you have:

  • Shortness of breath or trouble breathing
  • Swelling of your throat or tongue
  • Hives

What are the most common side effects associated with FIRDAPSE?

The most common side effects of FIRDAPSE include:

  • Tingling around the mouth, tongue, face, fingers, toes, and other body parts
  • Upper respiratory infection
  • Stomach pain
  • Diarrhea
  • Headache
  • Increased liver enzymes
  • Back pain
  • High blood pressure
  • Muscle spasms

Tell your doctor if you have any side effect that bothers you or that does not go away. These are not all the possible side effects of FIRDAPSE.

Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.


In conjunction with the FDA, Catalyst Pharmaceuticals has created a registry to collect information about the safety of FIRDAPSE use in the event of pregnancy. Patients with LEMS—even those not taking FIRDAPSE—may enroll. Contact the registry as soon as you learn that you are pregnant by calling 1-855-212-5856 or visiting

Help us track the safety of FIRDAPSE use during pregnancy. Contact the FIRDAPSE Pregnancy Registry by calling 1-855-212-5856 or visiting