What are the long-term side effects of taking allopurinol?

Favorable: In most cases it is very well tolerated and controls the production of uric acid reducing the frequency of gouty attacks and eliminating urate deposits around joints called tophy. It can however cause a severe allergic reaction to the point of causing the outer skin to peel off as in severe burn so at first sign of a rash it should be stopped. This is a rare disorder but important to know.