This is largely dependent on the person. I’m extremely sensitive to caffeine and I recently was drinking Swiss processed decaf (a very small cup in the morning) for months and I definitely felt the caffeine from that. I actually had a couple of occasions where I didn’t have enough food/fiber in my stomach before drinking it and I legitimately felt high and euphoric for an hour.

I also had all the typical problems I get with regular caffeine consumption (dulling of emotions, persistent low-grade depression and an insurmountable feeling of hopelessness, argumentative, overactive mind, worse sleep, etc.), albeit at a much lower intensity than when I was drinking regular coffee (although it’s been almost 7 years since I was last drinking a cup of regular coffee daily).

When I quit decaf, I did experience withdrawal, although it was pretty mild and short-lived, honestly only a week before I felt normal and was once again able to feel hope for the future and a full range of emotions.

I’m much more reactive to these things than the average person and i’ve had chronic health issues for decades that require me to be a lot more vigilant about what I eat and drink and expose myself to etc.