Elavil
"I have a very high tolerance for a lot of pain medications due to pain issues. Your body always needs more and more to produce the same effect until almost nothing works. 

Fortunately, this type of medication doesn't affect me that way. Although I guess it is mainly used for depression. It has worked like a charm for me to get my body to sleep much longer. And I have never had to increase the dose. The only drawback for me with this medication is that when I do wake up I am pretty groggy for about 45 minutes."