What occurs when a drug binds to a receptor in the body?

When a drug binds to a receptor in the body, the receptor is activated or inactivated.

Molecules such as hormones, drugs or neurotransmitters that bind to a receptor are called ligands. The binding can be specific and reversible. A ligand may activate or inactivate the receptor; activation may increase or decrease a particular cell function. Each ligand may interact with multiple receptor subtypes.