While I don’t have hard evidence to support the idea, I believe this is highly variable between individuals.
I’m not a heavy coffee drinker, but I do have a cup in the mornings some time between 6:30-8:00. This makes it easy to stop as needed; there are some days where I skip it out of necessity (too busy), and occasionally I’ll go a weekend without it just to keep my tolerance in check. During these periods, I never experience adverse effects.
The main benefit I glean from coffee is not feeling awake, but notably improved ability to focus. In my experience, my baseline ability is just not as good; there’s no “bounce back” after extended periods of going without, it just stays somewhere between bad and average indefinitely.
I strongly suspect this manifests more in folks that consistently intake > 100mg per day. I used to regularly intake 200mg total across ~2 beverages (mostly because I just enjoyed the flavor), and suffered mild headaches if I skipped my schedule. I know others that start their day with 200mg in a single, quad shot beverage.
3 years ago I took a summer and then autumn off of caffeine; my intent was to quit and only use caffeine in "times of need". This would be an on-brand thing for me to do as a person, and something I wanted pretty bad. But after 4 full months without touching any caffeine, my mood/energy levels never returned or even really rebounded any further than they did after the first month. I'm just a different person with caffeine, even after I'm addicted/habituated/develop tolerance. Notably I have a lot more energy, and I'm not a high energy person to start with. This energy allows me to better take care of myself, exercise, and be social, all things that I struggle with in its absence.
From experience, I can function fine without caffeine, even under an acute withdrawal scenario. In fact, some of my greatest achievements were done without caffeine for one reason or another. Not having caffeine just makes those things more miserable in the moment, at least for me.
This makes me so tempted to get one of those whole genome tests. I had issues with anxiety from age 20 to 38. I was a regular drinker of coffee between the age 20 to 38. About a month after quitting I was finally able to yawn properly like I remember I was able to when I was young. Coffee overstimulates me I figure.
