Preventive medicines are used to avoid severe or chronic headaches, such as migraines or cluster headaches. They are not usually used to treat headaches after they begin.
Preventive medicines relax blood vessels. Some headaches may be caused by narrowing or tightening of blood vessels.
Examples of preventive medicines are beta-blockers, calcium channel blockers, antidepressants, and anticonvulsants.
In order for these medicines to work, you will need to take them daily even when you do not have a headache. You may have to take them daily for only a few months.
WebMD Medical Reference from Healthwise