Your Guide to Interferons

Medically Reviewed by Minesh Khatri, MD on August 30, 2022
4 min read

Interferons are proteins that are part of your natural defenses. They tell your immune system that germs or cancer cells are in your body. And they trigger killer immune cells to fight those invaders.

Interferons got their name because they "interfere" with viruses and keep them from multiplying.

In 1986, the first lab-made interferon was created to treat certain types of cancer. It was one of the earliest treatments to work with your immune system to fight illness and was later approved as a treatment for several other conditions, including hepatitis and multiple sclerosis.

Almost every cell in your body makes interferons. There are three main types:

  • Interferon-alpha (or interferon-alfa)
  • Interferon-beta
  • Interferon-gamma

Cells that have been infected with viruses or other germs give off interferon-alpha and interferon-beta as a warning signal to your immune system. That triggers immune cells called white blood cells to release interferon-gamma to fight the germs.

Interferons work in a few different ways. They:

  • Alert your immune system so it can go after the virus or cancer
  • Help your immune system recognize the virus or cancer
  • Tell immune cells to attack
  • Stop virus and cancer cells from growing and dividing
  • Help healthy cells fight infection

Interferon-alpha treats viral infections, including:

  • Chronic hepatitis C, hairy cell leukemia, Kaposi sarcoma caused by AIDS, chronic myelogenous leukemia (CML)
  • Chronic hepatitis, lymphoma, and malignant melanoma
  • Genital warts

But interferons aren't used as often to treat these diseases; newer drugs have come along that work better and faster. 

Interferon-beta treats different types of multiple sclerosis. It eases inflammation in your brain and spinal cord to prevent nerve damage.

Interferon gamma-1b (Actimmune) treats chronic granulomatous disease, which affects the way your immune system works, and severe malignant osteopetrosis, which affects your bones.

Certain types of interferon medications have a chemical called polyethylene glycol (PEG) added to them. PEG makes the medicine last longer in your body, so you don't need as many shots.  These are called peginterferon drugs.

You get interferon as a shot under your skin or into a muscle. A doctor can give you the shot or teach you how to give it to yourself at home. Interferon is also sometimes given through a vein in your arm (infusion).

The number of shots or infusions you need depends on the condition you have. Shots are often given three times a week, but to treat cancer, you may get an infusion 5 days a week for several weeks or months.

Interferons are man-made versions of proteins your body makes. These drugs work with your immune system to help it find and attack viruses and cancer. They can stop virus and cancer cells from growing and spreading, and prevent other cells from getting infected.

If you have MS, they can make you less likely to have a flare-up and slow damage to your brain and spinal cord.

Interferons can cause some health issues, including:

Heart problems. A small number of people who are treated with interferons can have a fast or irregular heartbeat or low blood pressure.

Mental health conditions. Some people have said they feel depressed or think about suicide while taking interferon. If you have depression or another mental health disorder, your doctor might need to watch you more closely while you take one of these drugs.

Eye disease. Interferons could make some eye diseases worse. Everyone should have a vision check before starting on these drugs. People with diseases like diabetic retinopathy will need to have regular eye exams while they're being treated with interferons.

Thyroid disease. In rare cases, interferons can make the thyroid gland overactive (hyperthyroidism) or underactive (hypothyroidism). If you have thyroid disease that's not well controlled with medicine, you may not be able to take interferon. Before you start treatment, your doctor will check your thyroid hormone levels.

Lung disease. Interferons can sometimes make lung problems like shortness of breath, pneumonia, and bronchitis worse. People with lung disease should be watched closely by a doctor while taking these drugs. If you have symptoms like a cough or shortness of breath, you might need to stop taking this medicine.

Common side effects from interferons include:

  • Pain, redness, and swelling where you get the shot
  • Flu-like symptoms
  • Tiredness
  • Fever
  • Chills
  • Muscle pain
  • Low back pain
  • Joint pain
  • Headache
  • Loss of appetite
  • Weight loss
  • Nausea, vomiting
  • Dizziness
  • Nervousness
  • Hair loss
  • Higher chances of infection
  • Weakness
  • Pale skin
  • Bruising or bleeding more easily than usual
  • Shortness of breath
  • Diarrhea
  • Trouble sleeping
  • Rash
  • Depression
  • Confusion

Some of these side effects, including flu-like symptoms, go away within a few hours after you get the injection.

These side effects are less common:

  • Chest pain
  • Rash
  • Liver problems
  • Change in taste
  • Belly pain
  • Trouble getting pregnant
  • Loss of sex drive
  • Lack of periods
  • Thirst
  • Dry mouth
  • Constipation
  • Swollen glands
  • Flushed skin
  • Sweating

These side effects are rare:

  • Shaking
  • A feeling like pins and needles

Interferons may not be safe for certain groups of people.

Pregnant and breastfeeding women. Some interferons can harm an unborn baby. Your doctor may recommend that you have a pregnancy test before you go on interferons and use protection -- like condoms -- for as long as you take it. Interferon can also get into your breast milk, so don’t breastfeed while you take it.

Men who are trying to get their partner pregnant. These drugs can cause birth defects if the father is taking it when their partner gets pregnant. You shouldn't father a child for at least 6 months after you finish treatment.

Interferons can sometimes affect how other medicines work. Tell your doctor about all the other drugs you take -- including vitamins, supplements, and drugs you bought over-the-counter without a prescription -- before starting on this treatment.

Talk with your doctor about how long you should wait before getting any live vaccines such as those for the chickenpox or measles, mumps and rubella (MMR). These have live but weakened forms of the disease. Since interferon affects your immune system, it can raise your risk of getting sick with the diseases that these vaccines are supposed to prevent.