Lemtrada Side Effects

Side effects of Lemtrada range from rash, headache and fever to thyroid disorders, infections, and serious, sometimes fatal autoimmune conditions. In November 2018, the FDA added its strongest warning to the drug’s label about stroke and tears in arteries in the head and neck.

Lemtrada Side Effect Facts
  1. Common Side Effects: Rash, headache, fever, cold-like symptoms, nausea, urinary tract infection, fatigue, insomnia
  2. Black Box Warning Autoimmunity, infusion reactions, stroke, malignancies
  3. Distribution Restricted Because of the risk of serious side effects, the drug is only available through the Lemtrada Risk Evaluation and Mitigation Strategy (REMS) Program.

From 2014 to March 31, 2019, Americans reported 3,839 cases of adverse events related to Lemtrada. Of those, 2,825 were serious, including 119 deaths, according to the FDA Adverse Events Reporting System (FAERS).

Because of the possibility for serious side effects, the drug is only available through a restricted distribution program called the Lemtrada Risk Evaluation and Mitigation Strategy (REMS) Program.

Lemtrada is available only through the Lemtrada Risk Evaluation and Mitigation Strategy (REMS) Program, a restricted distribution program to help ensure that the medicine’s benefits outweigh the risks.
Source: U.S. Food and Drug Administration

On Nov. 29, 2018, the U.S. Food and Drug Administration warned about rare but serious risks of stroke and tears in blood vessel walls with Lemtrada.

Lawyers are filing lawsuits against Lemtrada’s manufacturer, Sanofi Genzyme, on behalf of people who suffered ischemic stroke, hemorrhagic stroke, head or neck (cervicocephalic) arterial dissection, or death due to these complications.

Rash, Headache and Other Common Side Effects

Common side effects of Lemtrada can happen immediately after taking the drug. They are typically less serious and may go away after a short time.

In controlled clinical trials, researchers studied the drug in 811 patients with relapsing forms of MS and compared it to treatment with interferon beta-1a. The most common side effects occurred in at least 10 percent of participants and happened more often in the group that had received Lemtrada.

Common side effects include:
  • Abdominal pain
  • Arthralgia
  • Back pain
  • Diarrhea
  • Dizziness
  • Fatigue
  • Flushing
  • Fungal infection
  • Headache
  • Herpes viral infection
  • Insomnia
  • Nasopharyngitis
  • Nausea
  • Oropharyngeal pain
  • Pain In extremity
  • Paresthesia
  • Pruritus
  • Pyrexia
  • Rash
  • Sinusitis
  • Thyroid gland disorders
  • Upper respiratory tract infection
  • Urinary tract infection
  • Urticaria
  • Vomiting

Sanofi Genzyme and the FDA gathered more data about postmarketing side effects of Lemtrada. Postmarketing reports come from people who used the drug after it hit the market. These reports are voluntary, and there is no way to verify how many people may have suffered these reactions or if the drug caused them.

Reported postmarketing side effects include gastrointestinal system disorders, pulmonary system disorders, blood and lymphatic system disorders, stroke and opportunistic infections.

Stroke and Blood Vessel Tears

In November 2018, the FDA released a safety communication warning about a rare but serous risk of stroke and tears in the lining of the arteries in the head and neck with Lemtrada. These tears are called arterial dissections. These conditions can lead to permanent disability or death.

Most of the people who suffered these complications developed symptoms within one day of receiving the drug. One patient had symptoms three days after treatment.

Infographic about artery dissection
Lemtrada can cause tears called dissections in the arteries of the neck and head.

Worldwide, there have been 13 cases of ischemic and hemorrhagic stroke or arterial dissection that occurred shortly after a patient received Lemtrada. Twelve of these cases happened within one day of receiving the drug.

The agency required Sanofi Genzyme to include the risk of stroke in the drug’s black box warning.

On April 12, 2019, the European Medicines Agency (EMA) initiated a review of Lemtrada after it received reports of problems with the heart and blood vessels occurring within one to three days of treatment. These include bleeding in the lungs, heart attack, stroke and arterial dissection in the neck and head.


Lemtrada’s prescribing information has a black box warning for autoimmunity. This means the drug can cause autoimmune disorders. Some can be serious and life-threatening. They include kidney, liver and thyroid problems, and immune thrombocytopenic purpura, a condition in which the body attacks platelets.

People who take the drug have an almost 50 percent risk of developing an autoimmune disorder, according to researchers from Queen Mary University of London. The researchers based their findings on unpublished data from Lemtrada’s phase III clinical trials.

People who take Lemtrada have close to a 50 percent risk of developing an autoimmune disorder that may be serious or fatal.
Source: Queen Mary University of London

The researchers discovered that when Lemtrada removes B and T immune cells to reduce MS symptoms, the B cells repopulate quickly while T cells do not. They theorize this causes the autoimmune responses.

Thyroid Disorders

In clinical trials, 36.8 percent of people treated with Lemtrada suffered thyroid disorders, according to the drug’s label. Newly diagnosed thyroid disorders continued to occur more than seven years after the first dose.

Of these thyroid disorders, about 5.2 percent were serious and included psychiatric and cardia events. Some people required surgery to remove bones and fat in the eye to treat eye bulging (orbital decompression) and to remove the damaged thyroid.

Inflamed thyroid gland
About 37 percent of people in Lemtrada clinical trials suffered a thyroid problem.

These thyroid disorders are especially dangerous to pregnant mothers. Thyroid antibodies can pass to the fetus. One baby developed Grave’s disease after its mother took Lemtrada while pregnant.

Immune Thrombocytopenic Purpura (ITP)

About 2 percent of patients who took Lemtrada suffered immune thrombocytopenic purpura, or ITP. This is a disorder in which the immune system attacks and destroys platelets.

Low platelet counts can lead to severe bleeding that may cause life-threatening problems. Bleeding may occur in the brain. One patient died from intracerebral hemorrhage in clinical trials. The drug can also cause low red and white blood cell counts.

Infusion Reactions

Infusion reactions are common and potentially serious side effects of Lemtrada. Only people trained to handle these reactions can administer the drug.

In clinical trials, 92 percent of people who received Lemtrada experienced a reaction, and 3 percent of the reactions were serious. Mild reactions included nausea, hives, itchy skin, insomnia, chills, temporary reddening of the skin, fatigue, difficulty breathing, pulmonary infiltrates, reduced ability to taste, indigestion, dizziness and pain.

These reactions typically happen during the infusion, but some can happen more than 24 hours after infusion.

Serious reactions in clinical trials included:
  • Anaphylaxis, including anaphylactic shock, in two patients
  • Angioedema
  • Bronchospasm
  • Hypotension
  • Chest pain
  • Bradycardia
  • Tachycardia, including atrial fibrillation
  • Transient neurologic symptoms
  • Hypertension
  • Headache
  • Pyrexia
  • Rash

In order to prevent or lessen the severity of infusion reactions, health care providers administer corticosteroids at least three days prior to Lemtrada treatment. They may also administer antihistamines and anti-fever medications.


Lemtrada may cause an increased risk of cancer, including thyroid cancer and melanoma, according to the drug’s black box warning. The warning advises patients to have a skin exam before treatment to get a baseline and to continue exams yearly after that.

Thyroid Cancer

According to clinical study results reported by Sanofi on the medication insert, three out of 919 patients treated with Lemtrada developed thyroid cancer compared to none in the group treated with beta-1a. In uncontrolled studies, two more Lemtrada-treated patients developed thyroid cancer.

The medication insert tells doctors and patients to look for signs of thyroid issues, such as a new lump or swelling in the neck and pain in the front of the neck.


In studies, five out of 1,486 patients treated with Lemtrada developed melanoma, according to the medication insert. One of those patients had advanced cancer.

Patients receiving the drug should have annual skin examinations.

Other Cancer Data

In contrast to the medication insert, a 2017 review published in Therapeutics and Clinical Risk Management by Dr. Cristina Guarnera and colleagues reports slightly different figures on malignancies.

Out of 1,486 patients treated with alemtuzumab, 29 developed malignancies.
  • Eight were thyroid cancers (six of these were stage 1 that developed 10 to 41 months after the last infusion).
  • Six were basal cell carcinomas.
  • Five were breast cancers.
  • Six were melanomas.
  • One patient died from non-EBV-associated Burkitt’s lymphoma.
  • Three patients developed Castleman disease.

In a follow-up study, 10 out of 100 patients developed precancerous or cancerous lesions.

Please seek the advice of a medical professional before making health care decisions.

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Michelle Llamas, Senior Content Writer
Written By Michelle Llamas Senior Writer

Michelle Llamas has been writing articles and producing podcasts about drugs, medical devices and the FDA for seven years. She specializes in fluoroquinolone antibiotics and products that affect women’s health such as Essure birth control, transvaginal mesh and talcum powder. Michelle collaborates with experts, including board-certified doctors, patients and advocates, to provide trusted health information to the public. Some of her qualifications include:

  • American Medical Writers Association (AMWA) Engage Committee and Membership Committee member
  • Centers for Disease Control and Prevention (CDC) Health Literacy certificates
  • Original works published or cited in The Lancet, British Journal of Clinical Pharmacology and the Journal for Palliative Medicine
Edited By

10 Cited Research Articles

  1. Baker, D. et al. (2017, August). Interpreting Lymphocyte Reconstitution Data From the Pivotal Phase 3 Trials of Alemtuzumab. Retrieved from https://jamanetwork.com/journals/jamaneurology/fullarticle/2630681
  2. DailyMed. (2019, January 22). LEMTRADA- alemtuzumab injection, solution, concentrate. Retrieved from https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=6236b0bc-82e9-4447-9a78-f57d94770269&audience=consumer#S5.2
  3. European Medicines Agency. (2019, April 4). Use of multiple sclerosis medicine Lemtrada restricted while EMA review is ongoing. Retrieved form https://www.ema.europa.eu/en/news/use-multiple-sclerosis-medicine-lemtrada-restricted-while-ema-review-ongoing
  4. Guarnera, C. et al. (2017). Alemtuzumab: a review of efficacy and risks in the treatment of relapsing remitting multiple sclerosis. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5522829/
  5. Queen Mary University of London. (2017, June 12). Retrieved from https://www.eurekalert.org/pub_releases/2017-06/qmuo-put061217.php
  6. Sanofi Genzyme. (n.d.). LEMTRADA REMS (Risk Evaluation and Mitigation Strategy) Program. Retrieved from https://www.lemtradarems.com/
  7. Sanofi Genzyme. (n.d.). Lemtrada Safety. Retrieved from https://www.lemtrada.com/about/safety-infusion-reactions
  8. Sanofi Genzyme. (n.d.). Secondary Autoimmune Event: Thyroid Disorders. Retrieved from https://www.lemtradahcp.com/autoimmunity
  9. U.S. Food and Drug Administration. (2018, November 29). FDA warns about rare but serious risks of stroke and blood vessel wall tears with multiple sclerosis drug Lemtrada (alemtuzumab). Retrieved form https://www.fda.gov/drugs/drug-safety-and-availability/fda-warns-about-rare-serious-risks-stroke-and-blood-vessel-wall-tears-multiple-sclerosis-drug
  10. U.S. Food and Drug Administration. (n.d.). FDA Adverse Event Reporting System (FAERS) Public Dashboard. Retrieved from https://www.fda.gov/drugs/fda-adverse-event-reporting-system-faers/fda-adverse-event-reporting-system-faers-public-dashboard
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