What are the known long term side effects for using tramadol on a daily basis?

Answer 1

in short:
SIDE EFFECTS: Tramadol is generally well tolerated and side effects are usually transient. Commonly reported side effects include nausea, constipation, dizziness, headache, drowsiness, and vomiting. Less commonly reported side effects include itching, sweating, dry mouth, diarrhea, rash, visual disturbances, and vertigo.

but for more info go here:
http://www.medicinenet.com/tramadol/article.htm

Answer 2

http://www.nlm.nih.gov/medlineplus/druginfo/uspdi/202789.html