Tiredness, swelling ankles/feet/hands, itchy skin, nausea, vomiting, abdominal pain, or trouble sleeping may occur. If any of these effects last or get worse, tell your doctor or pharmacist promptly.

People using this medication may have serious side effects. Some of these effects may occur even after stopping treatment. However, you have been prescribed this drug because your doctor has judged that the benefit to you is greater than the risk of side effects. Careful monitoring by your doctor may decrease your risk.

Tell your doctor right away if you have any serious side effects, including: headache that is unusual or doesn't go away, new/worsening cough, shortness of breath, diarrhea with blood/mucus, symptoms of liver disease (such as nausea/vomiting that doesn't stop, loss of appetite, stomach/abdominal pain, yellowing eyes/skin, dark urine), signs of kidney problems (such as change in the amount of urine, pink/bloody urine), dizziness/fainting, vision changes, deepening of the voice, eye redness/pain, sensitivity to light, numbness/tingling of the arms/legs, joint stiffness/pain, muscle weakness/tenderness/pain, signs of infection (such as sore throat that doesn't go away, fever, chills, burning/painful/frequent/urgent urination), easy bruising/bleeding.

Pembrolizumab may cause hormone gland problems (such as thyroid, pituitary, adrenal, pancreas). Your body could make too much or too little hormone. Tell your doctor right away if you have any symptoms such as: cold or heat intolerance, unexplained weight loss/gain, mental/mood changes, slow/fast/pounding/irregular heartbeat, unusual tiredness, constipation.

This medication may rarely make your blood sugar rise, which can cause or worsen diabetes. Tell your doctor right away if you have symptoms of high blood sugar such as increased thirst/urination. If you already have diabetes, check your blood sugar regularly as directed and share the results with your doctor. Your doctor may need to adjust your diabetes medication, exercise program, or diet.

Get medical help right away if you have any very serious side effects, including: chest pain, seizure.

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.