What is an agonist?

An agonist is defined as a substance that binds to a receptor and activates it, leading to a biological response. This mechanism is crucial in pharmacology because agonists mimic the action of naturally occurring substances in the body, such as hormones or neurotransmitters. When an agonist binds to its specific receptor, it triggers a conformational change in the receptor that initiates a series of cellular processes, resulting in a physiological effect.

For instance, in the case of a drug that acts as an agonist at a specific receptor, it would enhance the normal activity that the receptor is responsible for, leading to effects such as increased heart rate when binding to adrenergic receptors. Understanding the role of agonists is fundamental in developing therapeutic agents that can effectively modulate various physiological pathways in the body.

The other provided options describe different pharmacological concepts, such as antagonists which block receptor activity or other mechanisms affecting metabolism or absorption, but they do not accurately depict the function of an agonist.