Non-Steroidal Aromatase Inhibitors (NSAIs) are one of two categories of aromatase inhibitors (AIs). AIs are divided into two categories, steroidal aromatase inhibitors (SAIs, type 1 inhibitors) and non-steroidal aromatase inhibitors (type 2 inhibitors) that is based on their mechanism of action and structure. NSAIs are mainly used to treat breast cancer in women. NSAIs binding is a reversible process where NSAIs binds to the aromatase enzyme through non-covalent interactions. When aromatase inhibitors (AIs) are used to treat breast cancer the main target is the aromatase enzyme which is responsible for the high estrogen level.