In order for drugs to activate receptors, what must they have?

• A. High molecular weight
• B. Rapid metabolism only
• C. Both great affinity and intrinsic activity
• D. High lipophilicity only

Answer: (C)

To activate a receptor, a drug must both bind to the receptor and produce a response. That means it needs affinity (the ability to bind tightly) and intrinsic activity (the ability to turn on the receptor and generate a signal). If a drug binds but doesn’t activate the receptor, it blocks or dampens signaling. If it binds well and activates strongly, you get a full effect. If it binds well but only partially activates the receptor, you get a partial effect. So the best answer is that activation requires both high affinity and intrinsic activity. The other options aren’t needed for activation: molecular weight, metabolism rate, or lipophilicity aren’t what determine whether a drug can turn the receptor on.