Midrin is a combination medication containing isometheptene (a vasoconstrictor), acetaminophen (an analgesic), and dichloralphenazone (a sedative), which collectively work to reduce cerebral blood vessel dilation and alleviate pain associated with cluster headaches. The drug's mechanism involves constricting blood vessels in the brain, reducing inflammatory responses, and providing sedative effects that can help interrupt the intense pain characteristic of cluster headache episodes.