Pemetrexed Injection 500mg is a chemotherapy medication used to treat certain types of cancer, such as mesothelioma and non-small cell lung cancer. It works by blocking the ability of certain cells to make certain proteins, which can slow down or stop the growth of cancer cells. This medication is given as an injection into a vein (intravenously) by a healthcare professional. Common side effects include nausea, vomiting, low blood cell counts, and hair loss.