This medication can decrease your body's ability to fight an infection. This effect can lead to very serious (possibly fatal) infections (such as fungal infections, bacterial infections including tuberculosis). You should have a tuberculosis (TB) skin test before and during treatment with this medication. Also tell your doctor your medical history, especially of past/recent/current infections. You should also tell your doctor if you have lived or traveled in areas where certain fungal infections (such as coccidioidomycosis, histoplasmosis) are common or if you have been near someone with tuberculosis. Tell your doctor right away if you develop signs of an infection while using this drug, such as sore throat or cough that doesn't go away, fever, chills, night sweats, painful/frequent urination, unusual vaginal discharge, white patches in the mouth (oral thrush). If you are diagnosed with TB, you must first be treated for it before you start certolizumab to prevent a serious TB infection. Though it is very unlikely to happen, there is a risk (especially in children/teens/young adults) of developing cancer (such as lymphoma, skin) due to this medication or due to your medical condition. Discuss the risks and benefits of treatment with your doctor. Tell your doctor right away if you develop symptoms such as fever that doesn't go away, unusual lumps/growths, skin changes, swollen glands, swollen or painful abdomen, unexplained weight loss, or night sweats.

Cough, sore throat, stuffy/runny nose, or joint pain may occur. If any of these effects last or get worse, tell your doctor or pharmacist promptly. Remember that this medication has been prescribed because your doctor has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects. Tell your doctor right away if you have any serious side effects, including: easy bruising/bleeding, swollen joints, rash on nose and cheeks, eye pain, vision changes, dizziness, numbness/tingling of arms/legs, seizures, new or worsening symptoms of heart failure (such as shortness of breath, swelling ankles/feet, unusual tiredness, unusual/sudden weight gain). Certolizumab may rarely cause serious (possibly fatal) liver disease in people exposed to hepatitis B virus. Your doctor may order blood tests and watch for symptoms during treatment and for several months after your last treatment. Get medical help right away if you have any symptoms of liver damage, including: nausea/vomiting that doesn't stop, stomach/abdominal pain, dark urine, yellowing eyes/skin. A very serious allergic reaction to this drug is rare. However, get medical help right away if you notice any symptoms of a serious allergic reaction, including: rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing. This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist. In the US - Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088 or at www.fda.gov/medwatch. In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.

Some products that may interact with this drug include: abatacept, anakinra, other drugs that weaken the immune system (such as azathioprine, cancer chemotherapy, cyclosporine). This medication may interfere with certain lab tests (such as aPTT tests), possibly causing false test results. Make sure lab personnel and all your doctors know you use this drug.