Acetaminophen (paracetamol) is a common over-the-counter pain reliever and fever reducer.
Dichloralphenazone is a mild sedative owing primarily to its hydrolysis product, chloral hydrate. Chloral hydrate, a schedule C-IV controlled substance, is a sedative/hypnotic drug that acts on the central nervous system to produce relaxation and decrease emotional stimuli that influence the perception of pain associated with headache.
Isometheptene is a vasoconstrictor, a drug that causes constriction (narrowing) of cerebral blood vessels.
The pathophysiology of vascular headaches, especially migraine, is thought to be related to dilation of these cerebral blood vessels, so drugs that act to constrict them are used in the treatment of these problems.
This drug is commonly used in the treatment of Migraine headaches and is currently available in the United States and United Kingdom by prescription only.