5-HT antagonists and is used for the prevention, but not the treatment, of migraine
headaches. Ergotamine (4.124), another ergot alkaloid, can be used for treating existing
migraines, since it probably acts as a vasoconstrictor. Ketanserin (4.125), a 5-HT 2
antagonist, is a clinically effective hypotensive agent that acts through a unique mech-
anism. Related compounds show anxiolytic activity. The diethylamide of lysergic acid,
LSD (4.126), is a widely studied and abused hallucinogen. (The acronym originates
from the German name: Lyserg-Säure-Diethylamid.)
256 MEDICINAL CHEMISTRY