anything more than 8 hours and I feel more tired when i wake up then I did when I went to sleep in the first place.4 a nite MINIMUM and 9 max.But I've gone for months on little more than 4 hours a nite Though I must admit I was pretty bitchy near the end.longest stright period without sleep for me was 4 days.Smoked a 1/4gm of meth with a freind.