LEMTRADA is a prescription medicine used to treat adults with relapsing forms of multiple sclerosis (MS). Because of its risks, LEMTRADA is generally used in people who have tried 2 or more MS medicines that have not worked well enough. It is not known if LEMTRADA is safe and effective for use in children under 17 years of age.


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Lemtrada Safety

A look at some of the potential side effects

When considering LEMTRADA as your relapsing MS medicine, it's important to discuss potential common and serious side effects with your healthcare provider.

LEMTRADA can cause serious side effects including autoimmune problems, infusion reactions, stroke, tears in your arteries that supply blood to your brain (carotid and vertebral arteries), some kinds of cancers, thyroid problems, low blood counts (cytopenias), inflammation of the liver, serious infections, inflammation of the gallbladder without gallstones (acalculous cholecystitis), and swelling of lung tissue (pneumonitis). Because of the risks of autoimmune problems, infusion reactions and some kinds of cancers, LEMTRADA is only available through a restricted program called the Risk Evaluation and Mitigation Strategy (REMS) Program.

In two 2-year clinical trials, LEMTRADA was studied in over 800 patients.

LEMTRADA can cause serious infusion reactions that may cause death. Serious infusion reactions may happen while you receive, or up to 24 hours or longer after you receive LEMTRADA. You will receive your infusion at a healthcare facility with equipment and staff trained to manage infusion reactions, including serious allergic reactions, and urgent heart or breathing problems. You will be watched while you receive, and for 2 hours or longer after you receive, LEMTRADA. If a serious infusion reaction happens while you are receiving LEMTRADA, your infusion may be stopped. 92% of patients experienced infusion reactions on LEMTRADA, 3% of these reactions were serious.

Tell your healthcare provider right away if you have any of the following symptoms of a serious infusion reaction during the infusion, and after you have left the healthcare facility:

  • swelling in your mouth or throat
  • trouble breathing
  • weakness
  • fast, slow, or irregular heartbeat
  • chest pain
  • rash

These are not the only possible side effects of LEMTRADA. Tell your healthcare provider if you have any side effects that bother you or don't go away.


To lower your chances of getting a serious infusion reaction, your healthcare provider will give you a medicine called corticosteroids before your first 3 infusions of a treatment course. You may also be given other medicines before, during, and after the infusion to try to reduce your chances of having infusion reactions or herpes viral infection.


These will be given to you right before your LEMTRADA infusion for the first 3 days of each round of treatment


Your healthcare provider may consider administering antihistamines and/or a fever reducer before, during, and after your LEMTRADA infusion


You’ll be given an antiviral with treatment and will continue it until your immune cells reach certain levels

Infusion reactions can occur despite pretreatment.

In addition some people have had serious and sometimes deadly strokes and tears in their arteries that supply blood to the brain within 3 days of receiving LEMTRADA. Get help right away if you have any of the following symptoms that may be signs of a stroke or tears in your carotid or vertebral arteries:

  • drooping of parts of your face
  • weakness on one side
  • sudden severe headache
  • difficulty with speech
  • neck pain