I know this post is old but I have to warn you. DON"T combine fentanyl and diphenhydramine. A friend of mine was also having trouble with sleeping. Unfortunately she'll never wake up again. Please consult with your doctors with every question before you combine anything. God Bless.
According to MedLinePlus (from the NIH) -
http://tinyurl.com/6m6msb
Don't use diphenhydramine (Benadryl) with/after Fentanyl.......
That's what the hospital folx told me when they were using Fentanyl for my surgeries.
Stan
Hi. Caution has to be exercised when using Fentora together with Diphenhydramine containing drugs. The combination may result in severe constipation and paralysis of the bowels (ileus). It could also cause you to have difficulty in coordinating movements, and may lead to excessive sleepiness and stupor, and respiratory depression.
If the Fentora is not controlling your pain adequately, the dose may need to be increased. But I don't think it's a good idea to mix it with Diphenhydramine.