[malfist]

Just because the halflife leaves a measurable amount in your system, doesn't mean that that amount is enough for measurable outcomes.

In your example, a 200 mg caffeine intake in the morning, least to 100mg at noon, 50mg at 5PM, 25mg at 10PM. Yes that means you still have 25mg of caffeine. But it's unlikely to have an outcome you can measure since it's below a minimum threshold.

[Mezzie]

This depends on your genetics - there are different groups of caffeine metabolizers. I'm in the group that's super sensitive to caffeine and I can feel effects from less than 20mg.

[malfist]

Sure, but you're consumption is probably lower.