Sumatriptan is used to treat the symptoms of migraine headaches (severe, throbbing headaches that sometimes are accompanied by nausea or sensitivity to sound and light). Sumatriptan is in a class of medications called selective serotonin receptor agonists. It works by narrowing blood vessels in the head, stopping pain signals from being sent to the brain, and blocking the release of certain natural substances that cause pain, nausea, and other symptoms of migraine. Sumatriptan does not prevent migraine attacks or reduce the number of headaches you have.