In medicine and biology, a receptor antagonist is a substance that inhibits the normal physiological function of a receptor. Many drugs work by blocking the action of endogenous receptor agonists such as hormones and neurotransmitters.
There are two kinds of receptor antagonists:
- Antagonists that compete with an agonist for a receptor are competitive antagonists. An example is the interleukin-1 receptor antagonist, IL-1Ra.
- Antagonists that antagonize by other means are non-competitive antagonists.
Antagonists stop agonists from acting on certain receptors by blocking them.
Respective to their mode of action, antagonists can be broken down into 3 distinct groups:
- Chemical antagonists work by inactivating another chemical, the agonist. An example of this is the chemical Dimercaprol (antagonist) being used to treat arsenic (agonist) poisoning.
- Pharmacokinetic antagonists are drugs that alter the way the body handles another drug.
- Physiological antagonists are two substances that act to oppose each other's effects. For example, noradrenaline (norepinephrine) will increase the heart rate while acetylcholine will decrease it, although these substances act upon different receptors. This is similar to the actions of insulin and glucagon.