Diphenhydramine (main ingredient) you will usually only find it in 25mg a pill. This is an antihistamine, which means it makes you tired.
It gives you a partially euphoric high, you have to take quite a few to get anywhere. (not posting a dosage)
You need a high tolerance of not letting yourself falling asleep.
Myself, I have been so messed up that I thought I saw stuff and hear things, but you have to know how to make your mind not think about it in a negative way, i.e. getting scared.
takes about 1-2 hours to hit you, and you might already be asleep by then.
Great way to avoid RC sleeplessness.