By Counterforce Health Team —

Understanding Tysabri (Natalizumab): A Powerful Option for MS and Crohn’s Disease

What Is Tysabri?

Tysabri (generic name: natalizumab) is a prescription medication used to treat:

  • Relapsing forms of multiple sclerosis (MS) in adults
  • Moderate to severe Crohn’s disease in adults who haven’t responded well to other treatments

Developed by Biogen, Tysabri was first approved by the U.S. Food and Drug Administration (FDA) in 2004 and remains one of the most effective therapies for reducing disease activity in MS and improving symptoms in Crohn’s disease.

How Does Tysabri Work?

Tysabri is a monoclonal antibody — a type of biologic medicine that targets specific molecules in the immune system.

In both MS and Crohn’s disease, the immune system mistakenly attacks healthy tissue:

  • In MS, it targets the protective covering of nerves in the brain and spinal cord.
  • In Crohn’s disease, it causes chronic inflammation in the digestive tract.

Tysabri works by blocking immune cells (white blood cells) from crossing into the brain or intestinal tissue. It does this by attaching to a protein called α4-integrin, preventing immune cells from causing inflammation and tissue damage.

How Is Tysabri Given?

Tysabri is administered as an intravenous (IV) infusion — meaning it’s given through a vein — once every four weeks.

Each infusion typically takes about one hour, followed by an observation period to monitor for any infusion reactions or side effects.

Because of safety monitoring requirements, Tysabri is only available through a special distribution program called the TOUCH® Prescribing Program in the U.S.

Common Side Effects

Like all medications, Tysabri can cause side effects. Some are mild and manageable, while others require close medical supervision.

Common side effects include:

  • Headache
  • Fatigue
  • Joint or limb pain
  • Nausea
  • Dizziness
  • Urinary tract infections
  • Respiratory infections

Infusion-related reactions — such as rash, itching, or shortness of breath — can also occur during or shortly after treatment.

A Serious but Rare Risk: PML

One of the most important safety concerns with Tysabri is the risk of a rare brain infection called progressive multifocal leukoencephalopathy (PML).

PML is caused by reactivation of the JC virus, which is harmless in most people but can cause severe brain damage in those with weakened immune systems.

Your healthcare provider will monitor you regularly for early signs of PML and may perform blood tests for JC virus antibodies before and during treatment.

Benefits of Tysabri

For many patients, Tysabri offers powerful and sustained results:

In multiple sclerosis:

  • Reduces relapse rates by up to 68%
  • Slows the formation of new brain lesions
  • Helps preserve mobility and daily functioning

In Crohn’s disease:

  • Reduces intestinal inflammation
  • Helps achieve and maintain remission
  • Improves quality of life for patients who have not responded to standard treatments

What to Expect During Treatment

Before starting Tysabri, your doctor will:

  • Review your medical history
  • Test for the JC virus
  • Discuss your risk factors and other medications

During treatment:

  • Infusions are given every 4 weeks at a certified infusion center.
  • You’ll be monitored for side effects during and after each session.
  • Your doctor may perform regular MRI scans (for MS) or lab tests (for Crohn’s) to track your progress.

Living Well on Tysabri

Many people on Tysabri report improved energy, fewer relapses or flares, and a better ability to live their lives normally. Staying consistent with infusions and maintaining regular check-ins with your care team are key to maximizing its benefits safely.

Tips for success:

  • Keep all scheduled appointments.
  • Report new or unusual symptoms right away (especially changes in vision, strength, or speech).
  • Stay informed about your JC virus status.

Final Thoughts

Tysabri (natalizumab) represents one of the most effective modern therapies for relapsing MS and Crohn’s disease. While it comes with some risks that require careful monitoring, its ability to dramatically reduce relapses and inflammation has made it life-changing for many patients.

If you or someone you love is considering Tysabri, talk with your healthcare provider about the potential benefits, side effects, and monitoring plan to determine if it’s the right fit for your treatment journey.