Along with its benefits, pirfenidone may cause some unwanted effects. The most common side effects include:

• nausea
• dyspepsia
• diarrhea
• vomiting
• fatigue
• weight loss
• dizziness
• rash and increased sensitivity to the sun.

Seek medical attention right away if you experience any of these side effects:

• Severe allergic reactions (rash; hives; itching; difficulty breathing; tightness in the chest; swelling of the mouth, face, lips, or tongue; wheezing)
• chest pain
• severe or persistent diarrhea, nausea, stomach pain or upset, or vomiting
• sunburn
• symptoms of liver problems (eg, bleeding or bruising more easily than normal, dark urine, pale stools, persistent loss of appetite, severe stomach pain, unusual tiredness, yellowing of the eyes or skin).

The way that perfenidone works is not fully understood. It may reduce inflammation and fibrosis in the lungs of patients with pulmonary fibrosis. It may prevent worsening of the condition and it may improve lung function.

Do not take pirfenidone:

•  If you are allergic to pirfenidone or any of the other ingredients in this medicin
• If you have severe liver disease
• If you have severe kidney disease 
• If you are taking:
  • fluvoxamine to treat depression and obsessive compulsive disorder (OCD)

Pirfenidone should be prescribed by and supervised by specialist physicians experienced in the diagnosis and treatment of IPF.

Cigarette smoking decreases pirfenidone's effectiveness. Patients should stop smoking before, and not smoke during pirfenidone therapy

Pirfenidone may cause you to become sunburned more easily. Avoid the sun, sunlamps, or tanning booths until you know how you react to pirfenidone. Use a sunscreen or wear protective clothing if you must be outside for more than a short time.

Pirfenidone should be used cautiously in patients with reduced liver or kidney function.

Use in pregnancy: not recommended.  

Use in breastfeeding: not recommended