Hi Baddog

I am unsure about adrenal fatigue. You might find this link (and links therein) helpful in deciding for yourself whether or not it exists; https://en.wikipedia.org/wiki/Adrenal_fatigue.

As far as possible interactions between caffeine, morphine and Gabapentin are concerned, the "Interactions Checker" at http://www.drugs.com/pro/ is a good place to start.