A serotonin antagonist is a drug used to inhibit the action at serotonin receptors.

Many of the most important medications of this class selectively act at the 5-HT3 receptor

5-HT3 receptor

The 5-HT3 receptor is a member of the superfamily of ligand-gated ion channels, a superfamily that also includes the neuronal nicotinic acetylcholine receptors , and the inhibitory neurotransmitter receptors for GABA and glycine...

, and thus are known as 5-HT3 antagonist

5-HT3 antagonist

The 5-HT3 antagonists are a class of medications that act as receptor antagonists at the 5-HT3 receptor, a subtype of serotonin receptor found in terminals of the vagus nerve and in certain areas of the brain....

s. However, other drugs such as ketanserin

Ketanserin

Ketanserin is a drug with affinity for multiple G protein-coupled receptors . Initially it was believed to be a highly selective antagonist for serotonin 5-HT2A receptors, however this is not true. Ketanserin only has moderate selectivity for 5-HT2A receptors over 5-HT2C receptors...

 act upon other types of serotonin receptors.

Antagonists of the 5-HT_2A receptor are sometimes used as atypical antipsychotic

Atypical antipsychotic

The atypical antipsychotics are a group of antipsychotic tranquilizing drugs used to treat psychiatric conditions. Some atypical antipsychotics are FDA approved for use in the treatment of schizophrenia...

s, with the typical antipsychotic

Typical antipsychotic

Typical antipsychotics are a class of antipsychotic drugs first developed in the 1950s and used to treat psychosis...

s being purely dopamine antagonist

Dopamine antagonist

A dopamine antagonist is a drug which blocks dopamine receptors by receptor antagonism. There are five known types of dopamine receptors in the human body; they are found in the brain, peripheral nervous system, blood vessels, gastrointestinal tract and the kidney.-Uses and examples:* Used as...

s.

'Ketanserine' blocks 5 HT2A,5 HT2C and alpha 1 receptors.
'Ondansetron,Dolansetron,Granisetron' are 5 HT3 receptor antagonist.they are efficacious in treating chemotherapy induced emesis.
'Clozapine' blocks 5 HT2A,5 HT2C,D4 receptors.
'Quetiapine' blocks 5 HT2A,5 HT1A,D1-2,HI,alpha 1 receptors.
'Methsergide' is 5 HT2A-2C antagonist and nonselective 5 HT 1 receptor blocker.it causes retrperitoneal fibrosis and mediastinal fibrosis.
'Cyproheptadine' blocks 5 HT2A, HI and it is a mild anticholinergic.
'Pizotifen' is a 5 HT2A-2C , H1 blocker and anticholinergic used for migraine prophylaxis

references Textbook of Pharmacology by H L Sharma