Interferons are medications that used to be standard treatments for hepatitis C.

However, newer treatments called direct-acting antivirals (DAAs) are now the standard of care for treating hepatitis C. This is largely because they’ve been shown to be more effective than interferons and to cause fewer side effects.

But if you’ve taken interferons in the past, you might still be seeking information on the side effects that may occur due to long-term hepatitis C treatment with interferons.

If so, read on to learn about possible long-term interferon side effects, including symptoms to watch for. You’ll also learn about hepatitis C and how interferons were used to treat it.

Interferon treatment for hepatitis C would typically last 24–48 weeks (6–12 months). Interferons caused many long-term side effects partly because of this long treatment time.

Using the drug for this length of time gave side effects a chance to develop and get worse.

Another reason for the long-term side effects was that interferons were often used with ribavirin to treat hepatitis C. Ribavirin further raised the risk of 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

If you have these side effects and you’re concerned that they relate to your interferon exposure, call your doctor. They can assess you and determine if the interferons or something else is causing your symptoms.

Some side effects from interferons 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 diseases, mood disorders, increased infections, and stroke.

Autoimmune diseases

Interferons can boost your body’s production of certain antibodies. Antibodies are cells that fight harmful substances in your body. Antibodies may mistake some of your healthy cells for invaders and attack them.

This can cause a range of autoimmune disorders, such as psoriasis, rheumatoid arthritis, and lupus.

Symptoms of autoimmune diseases can include:

  • decreased or increased energy levels
  • increased tiredness
  • fever
  • rash
  • changes in urination, such as an increased urge to urinate and a decreased amount of urine output
  • 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 after having received interferon therapy.

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 may 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. And if you already have infections, interferons can make them more serious.

Signs of a new infection include:

  • fever or chills
  • sore throat
  • burning feeling when urinating
  • body aches
  • flu-like symptoms
  • skin changes such as bruising, flaking, and redness

You may also experience worsened symptoms — like pain and itching — of old infections such as herpes or fungal infections.

Call your doctor if any of these symptoms appear suddenly or get worse. Levels of white blood cells typically return to normal when interferon therapy is stopped, alleviating the increased risk of infection.

Stroke

Interferons can cause increased blood pressure and heart rate, which are both risk factors for stroke. These actions can cause two types of stroke: ischemic and hemorrhagic.

An ischemic stroke occurs when a blood clot reduces the blood supply to the brain. Hemorrhagic strokes occur when a blood vessel in the brain leaks or bursts and damages brain tissues.

However, there’s also some data that suggests earlier treatment with interferons can reduce your long-term risk of stroke.

If you’ve been treated with interferons and are concerned about your stroke risk, talk with your doctor. Symptoms of a 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 a stroke, call 911 right away.

If you’ve recently received treatment with 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.

Interferons used to treat hepatitis C could have other serious side effects in addition to the boxed warning effects. These can include decreased blood cell counts.

With decreased blood cell counts, you have low levels of white blood cells, red blood cells, and platelets in your body. Typically, this effect reverses once interferon therapy is stopped.

Decreased blood cell counts occur because interferons can prevent your bone marrow (the tissue inside your bones) from working well. Your bone marrow produces your blood cells. If your bone marrow doesn’t work well, it may produce fewer blood cells.

In addition to increased infections (see above), decreased blood cell counts can cause the following serious effects:

  • anemia
  • bleeding problems
  • thyroid issues
  • vision disorders

Anemia

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. Levels of red blood cells typically return to normal when interferon therapy is stopped, which means anemia goes away.

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. Levels of platelets typically return to normal when interferon therapy is stopped.

Thyroid issues

Your thyroid gland helps all the cells in your body function well. Interferon can cause permanent damage to the thyroid gland, resulting in body-wide issues.

Some of the symptoms of thyroid dysfunction include:

  • increased or decreased energy levels
  • drastic weight gain or weight loss
  • excessive sweating
  • thinning of hair
  • feeling too hot or cold
  • nervousness, agitation, or anxiety

Call your doctor if any of these symptoms occur after receiving interferon therapy. You may need replacement thyroid hormone if your thyroid isn’t producing enough, or treatment to reduce the activity of an overactive thyroid gland.

Vision disorders

Vision problems can result from interferon therapy. Interferon can cause vision loss due to decreased blood flow to the eye, as well as bleeding within the retina.

Vision problems may start as:

  • blurred vision
  • decreased vision sharpness
  • increased spots in your field of vision

Call your doctor if any of these symptoms occur after receiving interferon therapy. These changes can be permanent if not appropriately addressed by an ophthalmologist.

When interferons and ribavirin were used as a combination treatment they could cause many side effects.

Many of these were similar to those of interferon alone, such as:

  • neutropenia (low levels of white blood cells)
  • thrombocytopenia (low platelet count)
  • anemia
  • infections
  • vision problems, such as retinopathy (disease of the retina), that can cause vision loss
  • aggravation of autoimmune disorders, such as rheumatoid arthritis or psoriasis
  • thyroid disease (hyperthyroidism or hypothyroidism)
  • sarcoidosis
  • neuropsychiatric effects, such as depression and irritability
  • flu-like symptoms
  • fatigue

Some side effects were common to both interferons and ribavirin:

  • rash with flaky, dry skin
  • nausea
  • harm to pregnancy (for 6 months after treatment ends)

And a few side effects were mainly caused by use of ribavirin. These included respiratory symptoms, such as a persistent cough.

If you were treated with interferon and ribavirin and have any of the symptoms described above, be sure to tell your doctor.

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

  • peginterferon alfa-2a (Pegasys)
  • peginterferon alfa-2b (Pegintron)
  • interferon alfa-2b (Intron A)

All three of these drugs are injected under the skin. This is called a subcutaneous injection. These types of interferons were often used with ribavirin.

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 would help stop the virus from multiplying, which helped 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 ribavirin. These drugs were used in an attempt to cure the hepatitis C infection. However, they were only effective some of the time.

Effective treatment with these medications would prevent liver disease and cirrhosis (scarring of the liver). In addition, effective treatment would decrease the risk of liver cancer and help prevent liver failure.

But today, interferons aren’t typically prescribed to treat hepatitis C. In recent years, DAAs have become available, and they have a cure rate of up to 99 percent. These drugs require a shorter treatment time and typically have fewer side effects than interferons. However, they’re very expensive, and most of them only treat certain types of hepatitis C.

The type of DAA your doctor might prescribe would depend on your insurance coverage and the type of hepatitis C you have. Some examples of DAAs include:

  • Harvoni
  • Mavyret
  • Zepatier
  • Epclusa

To find out more about the long-term side effects of interferon use for treating hepatitis C, talk with your doctor. They can tell you if symptoms you’re experiencing may be linked with previous treatment with interferons. They can also offer ways to help ease your symptoms.

And if your symptoms turn out to be caused by other medications you’re taking, your doctor can help with that, too. For instance, they may change your dosage or switch you to a different drug.

Whatever the cause of your symptoms, working with your doctor and sticking to your prescribed hepatitis C treatment plan can help you manage your condition and feel your best.