Interferon Therapy Side Effects

  • Isla Cogle BSc Immunology student, University of Glasgow
  • Harry White Master of Science - MS, Biology/Biological Sciences, General, University of Bristol, UK

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Interferon therapy is an important tool in medical treatment. It is renowned for its ability to treat viral infections and specific types of cancers by aiding the body’s immune response. However, behind its therapeutic efficacy, there is a whole landscape of potential side effects, ranging from mild, flu-like symptoms, to severe, life-threatening conditions. This article aims to provide an understanding of both the common and more serious side effects associated with this treatment. 


What are interferons?

Interferons (IFNs) are proteins which are produced by the body’s immune system in response to disease or injury, and play an important role in treating viral and bacterial infections. These proteins can activate a number of genes which are useful for antiviral responses, as well as signalling to the cells around them to increase defence measures.1

There are three main types of interferons. Alpha and Beta (IFN-a and IFN-B) are both classed as type I as they share many properties and functions. Interferon Gamma (IFN-y) is a type II interferon.2 Alpha and beta are the most commonly used in therapies, with alpha having the most functional uses. IFN-y is critical for immune responses but is rarely used in treatments.2

Why are interferons used as treatment?

Interferons play many roles within the body which helps protect us from infection and diseases. They are immunoregulatory, meaning they send messages to the immune system in response to danger, signalling an immune response and better equipping the body to fight off infection.3 

They can also be a preventative measure against certain cancers. INFs can inhibit angiogenesis. (the formation of new blood vessels) Angiogenesis can be a normal bodily function but is also used by cancer cells to spread throughout the body. They can also stop the growth of cancerous cells by inhibiting their division and causing cell death.3

What can interferons be used to treat?

Interferon therapy can be used to treat many conditions, and the type of interferon used will depend on the illness. 

IFN-a is the most commonly used interferon in medicine and can treat many types of cancers, including non-Hodgkin's lymphoma, chronic myeloid leukaemia, and renal cell carcinoma. It is also used for the treatment of chronic viral hepatitis, such as Hepatitis C and Hepatitis B.4 In chronic hepatitis, 50-75% of patients (depending on the strain present) respond well to IFN-a treatment, particularly when used with other treatments which keep the INF-a in the body for longer. This can even prevent further damage to the liver, sometimes even healing it to some extent.5

INFs are very helpful in the treatment of tumours. Both renal-cell carcinoma and cutaneous melanoma patients have shown an increase in survival rates and quality of life with interferon therapy. They are also used for life-threatening blood vessel tumours when steroids have failed.2

Interferon-beta is used less commonly but has been shown to be effective in the treatment of multiple sclerosis (MS). The use of intramuscular injections has decreased the rate of relapse of the condition, especially when used with other immune system-aiding medications.4

Interferon-gamma has not been found to have many clinical uses but is effective in the treatment of a genetic condition called chronic granulomatous disease.3 This is a disease where the immune system can’t function properly, leading to constant life-threatening infections. Interferon therapy can help boost the function of the immune system, helping it better deal with these infections.6 

Side effects 

There are many side effects associated with interferon therapy. Mostly, these are very mild and manageable, but there are cases where they can become severe, even inducing autoimmune diseases or neurological issues. This makes it extremely important to consider this option thoroughly with the help of medical professionals. 

Common side effects 

The most common side effects are very similar to flu-like symptoms.3 

These include: 

  • Fever and chills 
  • Headache 
  • Myalgia (muscle pain) 
  • Tiredness

These are usually easily managed with pain medication and rest, however, it is important to contact a doctor if you have any concerns about these symptoms as they may indicate something more serious. 

Gastrointestinal side effects

These are side effects that affect the digestive system and any associated organs. Gastrointestinal side effects are usually non-specific, meaning that the symptoms are very general and make it difficult to entirely attribute them to interferon therapy.7 However, there are enough reports of these cases to suggest there is a link between them. 

These symptoms include:

  • Nausea
  • Vomiting 
  • Abdominal pains 
  • Altered sense of taste
  • Anorexia 

In very rare cases, it may be linked to ischemic and ulcerative colitis in patients who have a genetic susceptibility to irritable bowel diseases.7 

Haematological side effects

A common side effect that impacts the blood is a reduced blood cell count.4 This occurs when there are too few blood cells circulating in the bloodstream, and there are different types depending on which type of blood cell is affected.

Low red blood cell count (anaemia): red blood cells are responsible for carrying oxygen around the body, so anaemia leads to a decreased oxygen supply to organs and tissues. Symptoms include weakness, fatigue, and pale skin.8

Low white blood cell count (leukopenia): this is a reduction in the number of circulating immune cells, which can affect the individual’s ability to fight infections.9

Low platelet count (thrombocytopenia): platelets are important for blood clotting, and those with this deficiency may have difficulties forming clots leading to increased bleeding and bruising.10

Dermatological side effects

Interferon therapy can cause a number of side effects affecting the skin, including rashes, hair loss (alopecia), and itching. This is thought to be caused by the effect of the immune system’s actions, particularly on the follicles of the hair.11 

There is often redness and itching around the site of the injection, which usually just lasts a few days. This is the result of the immune response to the injury of the injection. 

Neurological side effects 

The main neurological effects of interferon therapy are headaches and dizziness. These are usually mild and subside quickly.3 In rare cases, it can cause more severe neurological issues including:12

  • Disorientation 
  • Depression 
  • Difficulty speaking or writing 
  • Delirium 
  • Seizures
  • Psychosis

Mental health issues are rare side effects and are more likely to become severe if the individual has symptoms of it prior to treatment.12 It is very important to speak to a doctor about any mental health concerns before beginning this therapy.

Serious and rare side effects

In extremely rare cases, very severe side effects can occur. It is important to monitor for these carefully after receiving interferon therapy, as some of these can be life-threatening if not properly treated. These serious side effects include:4 

Some mild side effects, like fatigue, could be indicative of a deeper issue, such as endocrine dysfunction, neuropsychiatric disorders or autoimmune diseases so it is important to pay attention to all side effects, and seek medical advice for any concerns.12 


As a result of the extensive list of side effects, anyone suffering from the following conditions will likely be advised against interferon therapy.4 

As well as this, anyone who has been on immunosuppressive medication or has undergone an organ transplant should also consider the risks. This is because interferon therapy triggers inflammation in the body, and this can be dangerous for anyone with a compromised immune system and leads to an increased chance of rejection in transplants. 

There may be exceptions to this if the benefits will outweigh the risks.


  • Interferon therapy uses proteins made naturally by the body in order to improve immune responses to infections and some cancers
  • There are many benefits to interferon therapy, but there are also many side effects
  • The most common side effects are similar to flu symptoms, such as fever, chills, headache, myalgia, and tiredness
  • This therapy can have effects all over the body, including the gut, blood, brain, and skin, and may even have more serious effects, such as inducing autoimmune diseases or liver failure
  • Because of its nature, there is a long list of people who this therapy will not be suitable for


  • Samuel CE. Antiviral Actions of Interferons. Clinical Microbiology Reviews [Internet]. 2001 Oct 1;14(4):778–809. Available from:
  • Friedman RM. Clinical uses of interferons. British Journal of Clinical Pharmacology [Internet]. 2008 Feb 1 [cited 2020 May 17];65(2):158–62. Available from:
  • Miller CHT, Maher SG, Young HA. Clinical Use of Interferon-γ. Annals of the New York Academy of Sciences [Internet]. 2009 Dec 1 [cited 2020 Mar 27];1182:69–79. Available from:
  • Khanna NR, Gerriets V. Interferon [Internet]. PubMed. Treasure Island (FL): StatPearls Publishing; 2022. Available from:
  • Taylor MW. Interferons. Viruses and Man: A History of Interactions [Internet]. 2014 Jul 22;101–19. Available from:
  • Chronic Granulomatous Disease (CGD) | NIH: National Institute of Allergy and Infectious Diseases [Internet]. Available from:

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This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Isla Cogle

BSc Immunology student, University of Glasgow

Isla is an immunology student passionate about making science accessible to everyone. With years of experience as a science tutor and volunteer, she simplifies complex concepts and connects the public to current issues in medicine. Her dedication to education and medical communication drives her efforts to bridge the gap between research and public understanding, helping others to make informed decisions about their own health.

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