An agonist is a substance that binds to a receptor in the body and activates it, producing a biological response. This can include natural substances like hormones or neurotransmitters, as well as synthetic drugs. Agonists play a crucial role in various physiological processes, such as muscle contraction and mood regulation. In pharmacology, agonists are often used to mimic the effects of naturally occurring substances. For example, morphine is an agonist that binds to opioid receptors, providing pain relief. Understanding agonists is essential for developing medications that can effectively target specific receptors in the body.