I drink about 500mg of caffeine a day in coffee and it does nothing for me, as far as I can tell. It doesn’t help me wake up, and I can drink it at 9pm and sleep like a champ. I just drink it for taste and out of habit.
I thought I was an oddball but it’s actually pretty common:
About 10% of the human population are hyposensitive to caffeine. They process caffeine so efficiently that these people report taking large doses ( >500 mg) without much effect at all. Those hyposensitive can also consume caffeine shortly before bedtime and still get a good night’s sleep.Source
And it goes on to say I’m an idiot:
Hyposensitive people should evaluate the necessity of caffeine. If large amounts of caffeine do not create the desired effects such as wakefulness, alertness, and productivity, then we would question the benefits of consuming it. Since caffeine is toxic, large doses daily could be doing damage over time, which isn’t yet fully understood.Source
So that’s that. I’m slowly switching to decaf.