Which type of tolerance occurs when nerve cells become less sensitive to the drug's effects over time with repeated use?

• A. Tolerance
• B. Cross-tolerance
• C. Pharmacodynamic tolerance
• D. Metabolic tolerance

Answer: (C)

When nerve cells adjust so they respond less to the same amount of a drug after repeated use, the change happens at the site of action in the brain—receptors and downstream signaling. This is pharmacodynamic tolerance, where the cells become less responsive through processes like receptor desensitization or downregulation. That’s different from metabolic tolerance, which would involve the body breaking down the drug faster and lowering its blood levels, not changing how the cells respond. It’s also not about tolerance to a different drug, which would be cross-tolerance. So the described effect—reduced cellular sensitivity with repeated use—best fits pharmacodynamic tolerance.