okay first of all, it takes a shitttt load of LSD to overdose, its practically impossible. The LD50 of LSD in rats is like 12,000 ug. A single hit is like 10-40 ug i wud have to guess...You dont have to worry about overdosing. You should probably take 2 hits for your first trip. take them and see how you are feeling in an hour or so. If you feel the need, take one or two more hits...But I wouldnt go past that, as its not really necessary and its your first trip. Not sure about the back thing.....but I seriously doubt that