Keytruda is a brand name for the drug pembrolizumab, which is a type of immunotherapy used to treat various types of cancer. According to the sources provided, common side effects of Keytruda include fatigue, nausea, diarrhea, decreased appetite, rash, itching, cough, shortness of breath, fever, and chills. Additionally, Keytruda can cause more serious side effects, such as lung problems, liver problems, intestinal problems, hormone gland problems, kidney problems, skin reactions, and infusion reactions. Patients should contact their healthcare provider immediately if they experience any of these serious side effects. It is important to note that not all patients will experience these side effects, and the severity of side effects can vary from patient to patient. Patients should discuss potential side effects with their healthcare provider before starting treatment with Keytruda.