Interferons are used to treat several conditions, including hepatitis C. These drugs can cause serious side effects when used for long-term treatment. If your doctor has prescribed an interferon to help treat your hepatitis C, you may be wondering what side effects to expect. This article describes these side effects, including symptoms to watch for. It also describes hepatitis C and how interferons work to treat it.

Why interferons have long-term side effects

Interferon treatment for hepatitis C typically lasts 24–48 weeks (6–12 months). Interferons have many long-term side effects partly because of this long treatment time. It gives side effects a chance to develop and get worse. Another reason for the long-term side effects is that interferons are often used with ribavirin to treat hepatitis C. Ribavirin further raises the risk of side effects.

More common long-term side effects

The more common long-term side effects of interferons are typically less severe. These side effects can include:

  • swelling or other reactions at the injection site
  • flu-like symptoms such as headache, tiredness, and weakness
  • chills
  • fever
  • trouble sleeping
  • nausea
  • vomiting
  • diarrhea
  • irritability or other mood changes
  • muscle pain
  • low levels of white blood cells
  • loss of appetite
  • itchy skin

Boxed warning side effects

Some side effects are serious enough to be included in a boxed warning. A boxed warning is the most serious warning from the Food and Drug Administration (FDA). Side effects highlighted in the boxed warning include:

Autoimmune disease

Interferons can boost your body’s production of certain antibodies. Antibodies are cells that fight harmful substances in your body. These antibodies may mistake some of your healthy cells for invaders and attack them. This can cause a range of autoimmune disorders. These include psoriasis, rheumatoid arthritis, and lupus.

Symptoms of autoimmune disease can include:

  • decreased or increased energy level
  • increased tiredness
  • fever
  • rash
  • changes in urination, such as increased urges and decreased amount of urine
  • retaining water, with symptoms such as puffiness in your face, arms, or legs
  • pain or swelling in your joints

Call your doctor if you have any of these symptoms.

Serious depression and other mood disorders

Interferons can cause or worsen serious depression or other mental illness. The risk for each condition is higher if you’ve had that condition before. It’s not known why interferons can cause mood disorders.

Symptoms can include:

  • aggressive behavior
  • hallucinations (seeing or hearing things that aren’t real)
  • mania (feeling highly excited and restless)
  • thoughts of suicide

Call your doctor right away if you have serious mood changes, depression, or thoughts of suicide.

Increased infections

White blood cells fight infections as part of your immune system. Interferons can change the way white blood cells fight infection. Interferons can also slow cell growth, which can cause lower levels of white blood cells. Low levels of white blood cells can cause more frequent infections. If you already have infections, interferons can make them more serious.

Symptoms of increased infection can include:

  • signs of new infection, such as:
    • fever
    • rash
    • tiredness
    • congestion
    • pain
    • skin changes such as bruising, flaking, and redness
    • worsened symptoms of old infections such as herpes or fungal infections, including pain and itching

Call your doctor if infection symptoms appear or get worse.


Interferons can cause increased blood pressure and heart rate, which are risk factors for stroke. These actions can cause two types of stroke. They can cause ischemic stroke, which occurs when a blood clot reduces the blood supply to the brain. They can also cause hemorrhagic stroke, which occurs when a blood vessel in the brain leaks or bursts and damages brain tissues.

Symptoms of stroke can include:

  • changes in speech such as slurred speech or struggling to find words
  • headache
  • changes in vision such as blurry or double vision
  • confusion
  • weakness

If you think you’re having any symptoms of stroke, call 9-1-1 right away. When you start taking an interferon, tell your family about the possible risk of stroke from this drug. They can prepare to help you if you have stroke symptoms and cannot help yourself.

Other serious long-term side effects

Interferons used to treat hepatitis C can have other serious side effects in addition to the boxed warning effects. These can include decreased blood cell counts. If you have decreased blood cell counts, that means you have low levels of red blood cells, white blood cells, and platelets in your body.

This happens because interferons can prevent your bone marrow from working well. Your bone marrow produces your blood cells. If your bone marrow doesn’t work well, it may produce fewer blood cells. Lowered levels of blood cells can cause the following serious effects:

Increased infections

Your white blood cells fight infections. Having low levels of these cells can cause more frequent infections. Symptoms of increased infections can include:

  • fever or chills
  • sore throat
  • burning feeling when urinating
  • body aches
  • flu-like symptoms
  • worsened symptoms of old infections such as herpes or fungal infections, including pain and itching

Call your doctor if any of these symptoms appear suddenly or get worse.


Your red blood cells carry oxygen to other cells throughout your body. Reduced levels of red blood cells can cause anemia. Symptoms of anemia can include:

  • tiredness
  • weakness
  • pale skin
  • shortness of breath
  • irregular heart rhythm

Call your doctor if any of these symptoms appear suddenly or get worse.

Bleeding problems

Your platelets help your blood clot. Reduced levels of these cells can cause bleeding problems. Symptoms of bleeding problems can include:

  • increased bruising
  • increased bleeding from cuts
  • bleeding from your gums or nose
  • tiny reddish-purple spots on your skin
  • tiredness

Call your doctor if any of these symptoms appear suddenly or get worse.

More about interferons

Interferons are antiviral drugs, which means they fight viruses. The types of interferon used to treat hepatitis C are:

  • peginterferon alfa-2a (Pegasys)
  • peginterferon alfa-2b (Pegintron)

Both of these drugs are injected under the skin. This is called subcutaneous injection. These types of interferons are often used with ribavirin, which is also an antiviral drug. Your dosage and length of treatment for these interferons would be based on several factors. These factors include your weight, the type of hepatitis C you have, and whether you’re also taking other hepatitis C drugs.

How do interferons work?

Interferons work in a few ways. For one, they change the way white blood cells destroy invading cells. This change triggers the body’s built-in immune response to fight viruses such as hepatitis C. Interferons also help stop the spread of hepatitis C. Hepatitis C spreads by multiplying, or copying, its cells. Interferons help stop the virus from multiplying, which helps slow the spread of the virus.

Interferons have other broad actions that don’t target any virus in particular. This is one reason why these drugs can cause many side effects.

Why would my doctor prescribe interferons?

Until recently, treatments for hepatitis C focused on interferons and another drug called ribavirin. These drugs can’t cure hepatitis C. However, they can help you live more safely and comfortably with the disease. These drugs can help relieve symptoms, such as fever, tiredness, or pain in the abdomen. They can also help prevent liver disease and cirrhosis (scarring of the liver). In addition, they can decrease the risk of liver cancer and help prevent liver failure.

Within the last few years, newer drugs have become available that can cure hepatitis C. These drugs require a shorter treatment time and may have fewer side effects than interferons. However, these drugs are very expensive, and they only treat certain types of hepatitis C. As a result, doctors continue to prescribe interferons and other older medications in some cases.

About hepatitis C

Hepatitis C is an infection of the liver. It’s caused by the hepatitis C virus, a highly contagious virus that’s passed through the blood. There are six main types of hepatitis C (genotypes 1–6), which differ based on their genetic makeup. All types may occur in either an acute or chronic form. The acute form causes illness for a short time. But most people with hepatitis C develop the chronic, or long-lasting, form. Chronic hepatitis C is a serious condition that can lead to liver damage, liver cancer, and even death.

Keep reading: Chronic hepatitis C: Symptoms, diagnosis, and treatment »

Talk with your doctor

To find out more about the long-term side effects of interferons for hepatitis C treatment, talk with your doctor. They can tell you more about what to expect with use of these drugs. If you start taking an interferon and develop side effects, tell your doctor. They may offer ways to help ease your symptoms, or they may change your dosage. If your side effects are extreme, they may switch you to a different drug.

To be as healthy as possible, it’s important to finish your interferon treatment. Being aware of possible side effects and reducing them when possible can help you do that.