Not good.
I like the taste of coffee and certain carbonated drinks.
But it affects my head in subtle ways.
I used to drink coffee everyday out of pleasure.
As I grew older, I seem to be 'less tolerant'.
Not the energy aspects; I basically do not feel more awake as soon as I consume caffeine -- but with symptoms associated with being wired; tremors, heart palpitations, etc.
To a point that it can overwhelm me.
Now I quit taking caffeine on a regular basis, as sad for me to say good bye to the varying flavors of coffee and soft drinks...
I only can afford to take decaf. Caffeinated stuff can already affect me with few sips...
It varies with the brand, strength and quantity I consume in a single sitting.
Even with a single cup alone; ranging from diarrhea, insomnia, hyperacidity, tremors, restlessness, heart palpitations...
Sometimes my breathing patterns are affected, sometimes the way I relax. Sometimes it gives me brain fog. Sometimes headaches -- I'm not talking about withdrawals. Sometimes it did gave me a form of anxiety -- sometimes, I get the opposite.
While it can boost my mood for a moment, the effects for days would be emotionally more intolerant and easily more dysregulated.
Worst case is internal overwhelm, being numb in the inside. It is as if caffeine short circuited something in my head.