Definition of Agonist

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Agonist: A drug that binds to a receptor of a cell and triggers a response by the cell. An agonist often mimics the action of a naturally occurring substance.

An agonist produces an action. It is the opposite of an antagonist which acts against and blocks an action.

Agonists and antagonists are key agents in the chemistry of the human body and important players today in pharmacology.

For example, in treating Parkinson disease, the long-used drug levodopa can cause uncontrollable, jerky body movements called dyskinesias that can inhibit a person's ability to function. Dopamine agonists mimic the effects of dopamine in the brain by stimulating dopamine receptors with a lower risk of the uncontrollable and irreversible dyskinesias often associated with levodopa therapy.

There are agonists now for many of the known hormones. For example, LHRH (luteinizing hormone-releasing hormone) agonists are similar to LHRH in structure and are able to mimic the effects of LHRH, a hormone that controls sex hormones in both men and women.

The word "agonist" comes from the Late Latin agnista, contender, from the Greek agnists, contestant, from agn, contest. An agonist is a chemical contestant or contender.