I also have taken tramadol for lower back pain and just wanted to say NOT to take it along with an ssri or snri as it can result in serotonin syndrome which can be fatal. Any dosage of tramadol over 400mg per day can cause seizures. Please see your doctor and ask about switching (you'll need at least five days with no tramadol before you can start an anti-depressant) to an snri. My doctor put me on Cymbalta which can also help with the back pain.
Most of the reason it's hard to get off if is because it does have an snri effect and that's why most people have a hard time. I found it did work better than anything else for my back. The reason most doctors say it has a low addiction potential refers to its activity as a synthetic opioid. As far as comparison, 1 tramadol is equal in pain relief to 1 Tylenol 3.
Hope this helps.