depression
"Tramadol is NOT an opiate.  It does act on the same pain receptors as opiates, but it does not have the same addictive quality as opiates and does not have the same risk of abuse as opiates.  You can become dependent on Tramadol, just as you can be dependent on SSRI's.  You can't cold turkey quit an SSRI without some really gnarly withdrawal symptoms and the same goes for Tramadol and opiates and tons of other drugs.  

I've been taking Tramadol for 4 years for general pain in my body due to end stage renal disease and osteodystrophy.  Since I've been taking Tramadol I have not needed antidepressants and I find that I function at a higher level with Tramadol than with any SSRI I have ever taken.  There are no negative side effects for me."