"yes, i have experienced a side effect of ultram which is preventing me from sleeping. it has 50 mg 1 or 2 tablets every six hours as need. i have tried them from my doctor and i have been up all night, i had a total left knee replacement revision on the 8th of june, 2011. i was told also to take 1 ambien (10 mg) and 1 extra strength tylenol at the same time. i did and all i did was cat nap and was always awake when the daylight came up. i need rest!"