Editing Drug Receptor Theory (section)

== <span style="color: #FFFFFF;">Remembering</span> ==
* '''Receptor''' — A protein molecule on a cell's surface or inside a cell that "Recognizes" and "Responds" to a specific chemical.
* '''Ligand''' — Any molecule (a drug, a hormone, a neurotransmitter) that binds to a receptor.
* '''Agonist''' — A drug that "Turns ON" a receptor, mimicking the body's natural chemical.
* '''Antagonist''' (Blocker) — A drug that "Plugs" the receptor but doesn't activate it, preventing other messages from getting through.
* '''Affinity''' — How "Strongly" a drug sticks to its receptor (The "Magnetism" of the bond).
* '''Efficacy''' — How "Strongly" a drug activates the receptor once it is stuck there.
* '''Potency''' — The "Amount" of drug needed to get an effect (A "Potent" drug only needs a tiny speck).
* '''Selectivity''' — How "Pickily" a drug chooses its receptor (e.g., a "Selective" drug targets the lung but not the heart).
* '''Down-regulation''' — When a cell "Hides" its receptors because it is being overwhelmed by too many drugs (The cause of "Tolerance").
* '''Up-regulation''' — When a cell "Creates more" receptors because it is not getting enough messages (The cause of "Withdrawal").
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