Antagonists prevent receptor activation.
Bind to receptors, but do not activate them (no biological effects)  prevent agonists from binding  block action of agonists
Two types of antagonists:
1) Competitive
• bind to receptors reversibly  produce a “dilution” of receptors
• agonist is less potent – shifts the dose effect curve to the right
• maximum response still possible - effect can be overcome by higher dose of agonist

2) Non-competitive/irreversible
• reduces maximum response, as effect can not be overcome by increasing dose of agonist
• bind to the receptor site different from the agonist to block effect of agonist

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