BOTOX ® (onabotulinumtoxinA) is a prescription medicine that is injected to prevent headaches in adults with chronic migraine who have 15 or more days each month with headache lasting 4 or more hours each day in people 18 years or older. A migraine is a type of headache that may begin as a dull ache and then turn into a constant, throbbing pain, often felt on one side of the head. When you have a migraine, you may be sensitive to light and sound and experience nausea and/or vomiting. A migraine headache can last between 4 to 72 hours and may get worse by or cause you to avoid routine physical activities, such as walking or climbing stairs. If at least half of your month is made up of headache days, then you may be living with Chronic Migraine.