Serotonin receptor antagonist

A serotonin antagonist, or serotonin receptor antagonist, is a drug used to inhibit the action at serotonin (5-HT) receptors.
Types.
5-HT2A antagonists.
Antagonists of the 5-HT2A receptor are sometimes used as atypical antipsychotics (contrast with typical antipsychotics, which are purely dopamine antagonists). 
They include, but are not limited to:
5-HT3 antagonists.
Another subclass consists of drugs selectively acting at the 5-HT3 receptors, and thus are known as 5-HT3 antagonists. They are efficacious in treating chemotherapy-induced emesis and postoperative nausea and vomiting. 
They include, but are not limited to:
Other 5-HT3 antagonists are used for the treatment of irritable bowel syndrome:
Also, the antidepressant mirtazapine acts as a 5-HT3 antagonist.
Non-selective 5-HT antagonists.
Please note, that although some non-selective serotonin antagonists may have a particular affinity for a specific 5-HT receptor (and thus may be listed below e.g., methysergide), they still may also possess a generalised non-selective action. 
They include, but are not limited to: