An<unk>  is a histamine antagonist that serves to reduce or eliminate effects mediated by histamine, an endogenous chemical mediator released during allergic reactions, through action at the<unk>  receptor. Only agents where the main therapeutic effect is mediated by negative modulation of histamine receptors are termed<unk> s - other agents may have<unk> rgic action but are not true<unk> s.
In common use, the term<unk> " refers only to<unk> -receptor antagonists, also known as<unk> s. It has been discovered that these<unk> s are actually inverse agonists at the histamine<unk> -receptor, rather than antagonists per se.
H1 antihistamine
Anti inflammatory medications
Antagonist 
Non-steroidal anti-inflammatory drug
TNF inhibitor
Alpha blocker
PDE3 inhibitor
COX-2 inhibitor