Can A Person Have Diphenhydramine Before A Surgery?
Unless instructed not to, it should be ok.
Detailed Answer:
Hello and welcome,
This partly depends on the the type of anesthesia you will be having. If local or regional anesthesia, such as a spinal block, there really is no issue.
If general anesthesia, it should be ok if you have 6 or more hours between when you take the diphenhydramine and when you receive the anesthesia. Let the anesthesiologist (or intake nurse) know when you took the diphenhydramine and what dose.
Unless you were instructed specifically not to take any medications within a certain period of time, there shouldn't be a problem.
Regarding taking it after surgery: you should be given specific instructions post op. Likely you will still be somewhat sedated for awhile, or on pain medications which can be sleep inducing. But if that is not enough, ask about postoperative meds you can/can't take (and when), as that may be very specific for the surgery you are having.