Keytruda is a brand name for the drug pembrolizumab, which is a type of immunotherapy medication that is used to treat various types of cancer. While Keytruda has been shown to be effective in treating cancer, it can also cause side effects.

According to the Keytruda website [2], some of the most common side effects of Keytruda include fatigue, rash, itching, diarrhea, nausea, loss of appetite, constipation, joint pain, and cough. These side effects are generally mild to moderate in severity and can be managed with medication or other treatments. However, some patients may experience more serious side effects, such as pneumonitis (inflammation of the lungs), colitis (inflammation of the colon), hepatitis (inflammation of the liver), and endocrinopathies (hormonal imbalances).

Immunotherapy medications like Keytruda work by stimulating the immune system to attack cancer cells, which can also cause the immune system to attack healthy cells in the body. This can lead to autoimmune disorders, where the immune system attacks the body's own tissues and organs. Some of the autoimmune disorders that have been reported in patients taking Keytruda include hypothyroidism (underactive thyroid), hyperthyroidism (overactive thyroid), type 1 diabetes, and myasthenia gravis (a neuromuscular disorder).

It is important to note that not all patients will experience side effects from Keytruda, and the severity of side effects can vary from person to person. Patients should discuss the potential side effects of Keytruda with their doctor before starting treatment and should report any side effects they experience during treatment.

Sources:
[1] https://www.drugpatentwatch.com/p/biologics/tradename/KEYTRUDA
[2] https://www.keytruda.com/side-effects/
[3] https://www.cancer.net/navigating-cancer-care/how-cancer-treated/immunotherapy-and-vaccines/side-effects-immunotherapy