why the time that drugs like caffeine affect you are measured with “half life” regardless of the amount ingested rather than a constant rate

Question

Does the body not clear drugs like caffeine at a constant rate? If you drink less caffeine does the body clear it less quickly? Or am I not understanding it? Caffeine half life is about 5 hours (via Google), so regardless of if I drink 100mg or 900mg of caffeine, half (50mg or 450mg) will be left in my body 5 hours later? That seems like a pretty drastic difference in the rate of clearance.

In: 509

Answer 1

Essentially, you’re right. Most drugs are not metabolized at a constant rate, but instead as a half-life, called 1st order metabolism. Only a few drugs metabolized at 0 order metabolism which is a constant rate.