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

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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.

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Anonymous 0 Comments

Most drugs are eliminated at a rate proportional to the concentration of the drug in the blood. If you do the math for that, it works out to match the “inverse exponential function”. That is a fancy way to say “half life”.

The time of elimination for each half still left is constant.

Does that make sense?

If you have 100mg of caffeine, 50mg will be filtered out in 5 hours. Over the next 5 hours, 25mg will be filtered out. Over the next 5 hours 12.5mg will be eliminated. And so on and so on.

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