Is Diphenhydramine acceptable to use in Scientology?

Mainly used to sleep and allergies.

Depends. Do you plan on over dosing?

XD

It's Christian Science that's against medicine, not Scientology.

Scientology's the one with the alien psychic vampire spirits clinging to your body and causing your problems (but you only learn about them once you get to OT III; they start out by telling you it's suppressed traumatic memories, called "engrams", that cause your problems; then once you've "gotten rid" of your engrams, you have to get rid of all your past lives' engrams. THEN they tell you about the Body Thetans).

They're easy to confuse.

That would be totally up to the doctor and individual preferences. Scientology is not involved in medical practice.