Taken Benadryl to get high is great fun. I am 26 and have done plenty of "real" drugs in my time. I have done opiates, amphetamines, hallucinogens... the works. I feel pretty experienced in the drug world. One of my FAVORITE drugs is Diphenhydramine hydrochloride, more commonly known as Benadryl. I am 5'10" and 170 lbs. The first time I took them to get high I took about 15 25mg pills. It was a good experience, although there were sudden bouts of terror which quickly passed. The next time I took 20, and usually sick with that although I have taken 25. It creates a wonderful sense of delerium, where you're not sure if what you're thinking or hearing is real. I would say it is a hallucinogenic effect, although not so much visual as mental and auditory. It creates a wonderful physical effect in which you feel like the air has become water and you can float through it. I find myself waving my arms up and down slowly as if they were a fluid. The closest other drug I can compare that particular feeling to is Ecstasy. Your eyes may feel like they are bulging out of your face. It makes you feel extremely fatigued and wide awake at the same time. Eventually you will go to sleep but not pass out. It is a conscience decision. Typically I will sleep for 8-10 hours afterwards and find it hard to get up the next day, but once up it isn't so bad. I wouldn't recommend doing it when you have to be clear headed the next morning, but by lunch time you should be feeling about normal. Don't mix it with alcohol. I say this, however I do it at times. I say this mostly because I know my own personal limits however do not know what negative health effects I may be causing. I have noticed that there seems to be large bags under my eyes on a near permanent basis with what appear to be broken blood vessels below them. I also seem to develop a weird rosacea-like redness on my face. These seem to be the only major lasting effects.
Take at your own risk. It can kill you, as can most drugs worth doing. Be safe and do your homework.
Better living through chemistry.