Antagonists

Antagonists are drugs that block receptor activity, preventing the action of agonists or natural ligands.

Definition:

• An antagonist is a drug that binds to a receptor without activating it. It blocks the action of agonists (both drugs and endogenous substances).

Types of Antagonists:

1. Competitive Antagonist:

   • Binds reversibly to the same site as the agonist on the receptor.
   • Competes with the agonist for binding.
   • The effect of a competitive antagonist can be overcome by increasing the concentration of the agonist.
   • Example: Naloxone competes with opioids at opioid receptors.

2. Non-competitive Antagonist:

   • Binds either irreversibly to the receptor or to a different (allosteric) site.
   • Reduces the maximum response of the agonist, regardless of its concentration.
   • Example: Phenoxybenzamine, an irreversible α-adrenergic blocker.

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