Botox 100 IU Injection is used in treatment of Overactive bladder (OAB) symptoms, preventive treatment of migraine, cervical dystonia and muscle spasm. Botox 100 IU Injection is a protein made by a type of bacteria (Clostridium botulinum type A). It works by blocking the release of a chemical (acetylcholine). This temporarily weakens nerve activity in the muscles around your bladder and relieves symptoms such as urinary urgency and frequency. It also blocks pain signals in migraine and treats various types of involuntary muscle contractions.