Relpax (eletriptan) 40mg, 4 ftb is a prescription medication used to treat migraine headaches that have already started. It belongs to a class of drugs called selective serotonin receptor agonists, which work by narrowing the blood vessels in the brain. It is taken orally as a tablet and can be used within two hours of a migraine headache beginning, and should not be used more than once a day. Relpax should not be used for chronic daily headaches or for headaches occurring more than fifteen days per month. Possible side effects of Relpax include dry mouth, dizziness, tingling, nausea, and muscle weakness.