I can definitely relate, too. But not caffeine pills.
I used to take phentermine for weight loss. I still have some because I had to quit. A few days on those and it made me feel like electricity was running through my veins. But a few more days on them and I had tremors, sweating, heart palpitations and blood pressure of 170/95. Basically, going through the roof. The ER doctors thought I was on coke. Lol.

But yeah, I miss the high. But phentermine and one of my crazy meds, prozac, mess with serotonin. I know serotonin syndrome can be deadly, so it's not worth it.

Even knowing all of that, there are those days when I think, well, maybe just one little half wouldn't hurt me.....

So yeah, I can relate.