There are many different medicines that start with the letter I. These include ibuprofen, an anti-inflammatory medication; insulin, a hormone that helps regulate blood sugar levels; and ibuprofen, an pain reliever. In addition to these well-known medications, there are also many other medicines that start with the letter I. These include erythromycin, an antibiotic; isosorbide, a blood pressure medication; and iron supplements, which are used to treat iron deficiency. As this list shows, the letter I is a important part of the medical alphabet.