Even though it may be rare, some people may have very bad and sometimes deadly side effects when taking a drug. Tell your doctor or get medical help right away if you have any of the following signs or symptoms that may be related to a very bad side effect.
Signs of an allergic reaction, like rash; hives; itching; red, swollen, blistered, or peeling skin with or without fever; wheezing; tightness in the chest or throat; trouble breathing, swallowing, or talking; unusual hoarseness; or swelling of the mouth, face, lips, tongue, or throat.
A very bad brain problem called progressive multifocal leukoencephalopathy (PML) has occurred with dimethyl fumarate. It may cause disability or can be deadly. Tell your doctor right away if you have signs like confusion, memory problems, low mood (depression), change in the way you act, change in strength on 1 side is greater than the other, trouble speaking or thinking, change in balance, or change in eyesight.
Low white blood cell counts have rarely happened with dimethyl fumarate. This may lead to a higher chance of getting an infection. Tell your doctor if you have ever had a low white blood cell count. Call your doctor right away if you have signs of infection like fever, chills, or sore throat.
Liver problems have happened. Call your doctor right away if you get signs of liver problems like dark urine, feeling tired, not hungry, upset stomach or stomach pain, light-colour stools, throwing up, or yellow skin or eyes.
Tell all of your health care providers that you take dimethyl fumarate. This includes your doctors, nurses, pharmacists, and dentists.
Have blood work checked as you have been told by the doctor. Talk with the doctor.
Herpes zoster (shingles) and other severe infections have occurred with dimethyl fumarate. Sometimes, these infections have affected the brain, nerves, and other areas of the body. Talk with your doctor about what signs to watch for.
Tell your doctor if you are pregnant, plan on getting pregnant, or are breast-feeding. You will need to talk about the benefits and risks to you and the baby.