Erlotinib is a medication primarily used to treat certain types of cancer, particularly non-small cell lung cancer and pancreatic cancer. It works by inhibiting a specific protein called epidermal growth factor receptor (EGFR), which is often overactive in cancer cells, promoting their growth and division. By blocking this protein, Erlotinib helps slow down or stop the progression of the disease. This drug is usually taken orally in the form of a tablet and is often prescribed for patients whose cancer has specific genetic mutations that make them more likely to respond to EGFR inhibitors. Common side effects may include rash, diarrhea, and fatigue, and it is important for patients to discuss potential interactions with other medications with their healthcare provider.