I've done each once and it was purely out of curiosity. From what I've read the abuse of both Benodryl and Robitussin can cause severe health problems including irreversable liver damage (or was it kidney..:stoned: ).

Neither are something I expect to do often nor would I find it enjoyable to do often. And I don't recommend even trying Benodryl if you're curious. It's just not worth it. Try DXM if you must.