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Side Effects

Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor or nurse immediately if any of the following side effects occur:

More common

  • Body produces substance that can bind to drug making it less effective or cause side effects
  • Cough
  • Difficulty with swallowing
  • Dizziness
  • Fast heartbeat
  • Hives
  • Itching
  • Puffiness or swelling of the eyelids or around the eyes, face, lips, or tongue
  • Shortness of breath
  • Skin rash
  • Tightness in the chest
  • Unusual tiredness or weakness
  • Wheezing


  • Abdominal or stomach fullness
  • Blurred vision
  • Changes in behavior
  • Chest pain
  • Confusion
  • Difficult or labored breathing
  • Faintness or lightheadedness when getting up suddenly from a lying or sitting position
  • Feeling of warmth
  • Feeling unusually cold
  • Fever
  • Gaseous abdominal or stomach pain
  • Nausea
  • Redness of the face, neck, arms, and occasionally, upper chest
  • Shivering
  • Sneezing
  • Sore throat
  • Sweating
  • Thoughts of killing oneself
  • Troubled breathing
  • Yellow eyes or skin

Incidence not known

  • Back pain
  • Convulsions
  • Drowsiness
  • Headache

Some side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common

  • Bladder pain
  • Blistering, crusting, irritation, itching, or reddening of the skin
  • Bloody or cloudy urine
  • Cracked, dry, scaly skin
  • Diarrhea
  • Difficult, burning, or painful urination
  • Difficulty with moving
  • Discouragement
  • Feeling sad or empty
  • Frequent, strong, or increased urge to urinate
  • Irregular menstruation
  • Irritability
  • Itching of the vagina or genital area
  • Lack of appetite
  • Loss of appetite
  • Loss of interest or pleasure
  • Lower back or side pain
  • Muscle pain or stiffness
  • Pain during sexual intercourse
  • Pain in the joints
  • Pain, cramps, or heavy bleeding
  • Passing urine more often
  • Stomach pain
  • Stomach soreness or discomfort
  • Swelling
  • Swollen glands
  • Thick, white vaginal discharge with no odor or with a mild odor
  • Trouble concentrating
  • Trouble sleeping

Less common

  • Absent, missed, or irregular menstrual periods
  • Chest discomfort
  • Fainting
  • Local bleeding
  • Shakiness in the legs, arms, hands, or feet
  • Stopping of menstrual bleeding
  • Trembling or shaking of the hands or feet

Other side effects not listed may also occur in some patients. If you notice any other effects, check with your healthcare professional.

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


Your doctor will want to check your progress at 3 months and 6 months after the first injection, then every 6 months after that. Blood tests may be needed to check for unwanted effects.

Tell your doctor if you are currently taking interferon beta (Avonex®, Betaseron®, or Rebif®), azathioprine (Imuran®), 6-mercaptopurine (Purinethol®), cyclosporine (Gengraf®, Neoral®, or Sandimmune®), or methotrexate Rheumatrex® or Trexall®). Natalizumab should not be given together with these medicines.

This medicine may increase your risk of developing infections, including a rare and serious brain infection called progressive multifocal leukoencephalopathy (PML). Stop using this medicine and check with your doctor right away if you are having more than one of these symptoms: back pain, blurred vision, confusion, convulsions, difficulty with walking or other movements, dizziness, drowsiness, fever, headache, problems with vision or speaking, or unusual tiredness or weakness.

Natalizumab may cause a rare condition called immune reconstitution inflammatory syndrome (IRIS). This may occur after a person who gets PML stops using the medicine. Tell your doctor right away if you have an inflammatory reaction to an infection that includes mild burning, stinging, or tingling of the skin, or a feeling of heat, redness, or swelling of the skin.

Liver problems may occur while you are using this medicine. Stop using this medicine and check with your doctor right away if you are having more than one of these symptoms: abdominal pain or tenderness, clay-colored stools, dark urine, decreased appetite, fever, headache, itching, loss of appetite, nausea and vomiting, skin rash, swelling of the feet or lower legs, unusual tiredness or weakness, or yellow eyes or skin.

This medicine may cause a serious type of allergic reaction called anaphylaxis. Anaphylaxis can be life-threatening and requires immediate medical attention. Tell your doctor right away if you have a rash; hives; itching; swelling of the face, tongue, and throat; trouble breathing; or chest pain after you receive the injection.

Before Using

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For this medicine, the following should be considered:


Tell your doctor if you have ever had any unusual or allergic reaction to this medicine or any other medicines. Also tell your health care professional if you have any other types of allergies, such as to foods, dyes, preservatives, or animals. For non-prescription products, read the label or package ingredients carefully.


Appropriate studies have not been performed on the relationship of age to the effects of natalizumab injection in the pediatric population. Safety and efficacy have not been established.


Appropriate studies on the relationship of age to the effects of natalizumab injection have not been performed in the geriatric population. However, no geriatric-specific problems have been documented to date.


Pregnancy Category Explanation
All Trimesters C Animal studies have shown an adverse effect and there are no adequate studies in pregnant women OR no animal studies have been conducted and there are no adequate studies in pregnant women.


There are no adequate studies in women for determining infant risk when using this medication during breastfeeding. Weigh the potential benefits against the potential risks before taking this medication while breastfeeding.

Drug Interactions

Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. Tell your healthcare professional if you are taking any other prescription or nonprescription (over-the-counter [OTC]) medicine.

Other Interactions

Certain medicines should not be used at or around the time of eating food or eating certain types of food since interactions may occur. Using alcohol or tobacco with certain medicines may also cause interactions to occur. Discuss with your healthcare professional the use of your medicine with food, alcohol, or tobacco.

Other Medical Problems

The presence of other medical problems may affect the use of this medicine. Make sure you tell your doctor if you have any other medical problems, especially:

  • Liver disease—Use with caution. This medicine may make this condition worse.
  • Progressive multifocal leukoencephalopathy (PML; a rare virus infection of the brain that causes severe muscle disability)—People who have PML or who have ever had PML should not receive this medicine.
  • Weakened immune system (e.g., HIV infection, AIDS, leukemia, lymphoma, or organ transplant recipient)—This medicine is not recommended, because people with these conditions may be more likely to get infections including PML.


Natalizumab injection is used to treat patients with relapsing forms of multiple sclerosis (MS), and patients who have not been helped by other medicines. This medicine will not cure MS, but may delay physical disability and extend the time between relapses.

Natalizumab is also used to treat Crohn’s disease (CD) in patients who have not been helped by other medicines. This medicine will not cure CD, but may prevent it from occurring again.

This medicine is only available with your doctor’s prescription.