ive taken 500, 1000, and 1500mg doses of dramamine (dimenhydrinate- which is half benadryl half caffeine basically), so about 250, 500, and 750mg of benadryl and im @ 6ft. 165lbs. benadryl will make you tired, dramamine a little less so. 250mg of benadryl isnt much, weird feelings, restless leg syndrome (RLS), weird thoughts. 500mg will make you sensitive to sound and make you slip into boughts of thinking your in some other places talking a multitude of people (friends, family -- including dead), will make you possibly see stuff like bugs, wont be able to walk or talk too good, and will give you a nice full body rolling orgasm, though this much delirium might be a little scary. 750mg can be really scary and frustrating, ecspecially in the dark. it has all the above effects, plus the effect that you full on hallucinate shit the entire time to the point it pisses you off cause your thirsty as fuck and grab for a water bottle that isnt there. after a while of using the RLS goes away, atleast for me, and then it can be fun. always start low and work your way up of course.