No reaction it just wasn't doing anything. They add the allopurinol to shunt the aza into doing what it should do.
yeah I know it sort of magnifies the effects of it - actually it was mercaptoprine I had in the end... similar to AZA
first had a normal does of AZA - side effects...
then they tried me on mercaptopurine , though apparently a 50% chance of the same side effects with that one if you had them with AZA... unfortunately I did
then lastly I went to the low dose mercaptopurine to lessen the side effects (had to faff around with a pill cutter and take 1/4 of a tablet) + the allopurinol to boost it, was on that for a while until they switched me to humira