According to the US FDA (United State Food Drug Administration ) a boxed warning (sometimes "black box warning", colloquially) is a type of warning that appears on the package insert for certain prescription drugs, so called because the U.S. Food and Drug Administration specifies that it is formatted with a 'box' or border around the text.

Boxed warning side effects
Interferons have some side effects are too serious to enclose in boxed side effects. The boxed side effects of interferons are:

Autoimmune disease

Interferons have the potentiality to boost the production of certain antibody. Sometimes these antibodies are misunderstood with body’s healthy cell. This situation may lead to autoimmune diseases.

Symptoms of the 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

Serious depression and other mood disorders

Interferon also may cause serious depression and mental illness. Symptoms can include:

• Aggressive behavior
• Hallucinations (seeing or hearing things that aren’t real)
• Mania (feeling highly excited and restless)
• Thoughts of suicide

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: Symptoms of increased infection can include:

1. Signs of new infection, such as:
   • Fever
   • Rash
   • Tiredness
   • Congestion
   • Pain
2. Skin changes such as bruising, flaking, and redness
3. worsened symptoms of old infections such as herpes or fungal infections, including pain and itching

Stroke

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

In case of any kind of side effects including boxed warning, you will have to contact your doctors, pharmacist or healthcare professional.