psuedoephedrine is the active ingredient in benadryl. I wouldn't take it if you are not an advanced dxm tripper. I have researched both drugs extensively and concluded that for safety's sake, its a good idea not to take a combination of either unless you're taking light dosages of each (100-150 mg dxm, 100-150 mg, psuedo). Death is more common in combination overdoses rather than single drug overdoses also. If this is your first time, I'd recommend anywhere from 150 mg to 350 mg of dxm. Don't touch the psuedoephedrine until you've experimented with dxm a bit. The trip is a lot scarier.

www.third-plateau.org

That site should help you, just read their FAQ.