Anecdotal: If you aren't able to fall asleep as easily 6 hours after a cup of coffee vs 10 hours you might be a slow metabolizer.
Strangely enough, if you find yourself in this situation of having drank coffee too late in the day nicotine has actually been proven to speed up the metabolization of caffeine: https://www.ncbi.nlm.nih.gov/pubmed/3365914
I can usually drink coffee within an hour or two of bed. I don't normally do that but I can. On the weekends I drink 2 to 3 cups in the early morning around 5AM. Then around 2 pm I usually drink 1 to 2 more cups.
At 70 something my dad watched a TV show on ADD and said to my stepmom, I think I have ADD. He want to the doctor and told him the same. The doctor said, we don't test for ADD, instead we have assessment questions. He asked my dad, first question "How many cups of coffee do you normally drink?" Dad said 15 to 18 a day. Doctor said we are done. You have ADD.
He was on ritalin the rest of his life. I don't agree with having him on ritalin but that was not my choice. He died of old age at 83. Until a year before his death he had been very healthy. NEver got colds, the flu or anything like that. Had a little spring hay fever. That was all.
The way you present your doctor, if I told him I was taking 8 sleeping pills a day, he'd diagnose me with narcolepsy instead of telling me to cut back on the drugs.
My dad's doctor and not mine. Keep in mind this was antidotale from my dad. I'm sure the conversation was longer but that is how he (my dad) represented it.
Wow, I didn't know that. I gave up smoking a while ago and now think smoking is a terrible and costly habit/addiction, but I still miss smoking a cigarette while enjoying a nice cup of coffee.
I wonder if the metabolization benefits of nicotine actually made coffee more enjoyable on a physiological level.
An educated guess: you get stronger negative reactions to caffeine: anxiety/panic, aggression, insomnia, heart racing and/or palpitations, sweats, tremors/muscle spasms, dehydration.
That said, I don't think it's as genetically hard-coded as the the root comment suggested.
I've been through episodes (coinciding with when I was having debilitating symptoms of chronic fatigue and depression), when I experienced these symptoms (sometimes very severely) when consuming caffeine. As I've become more physically energized and mentally well, my tolerance for caffeine has vastly improved.
Strangely enough, if you find yourself in this situation of having drank coffee too late in the day nicotine has actually been proven to speed up the metabolization of caffeine: https://www.ncbi.nlm.nih.gov/pubmed/3365914