Imuran is tolerated by most who take it and has been used for decades so docs know this drug very well. A few react to it right away and have to stop taking it. The worst side effects can occur after taking it for a long time although not everyone has them. Azathioprine is a cytotoxin and can affect your wbc, rbc, and platelet counts so you must have blood work every few months or more often in the beginning. After 18 months it lowered wbc, rbc, platelets and I had to reduce the dosage. Took it for another 3 years and had no problems.
Imuran is a cake walk compared to prednisone and most people do well on it. One negative is that it takes months before it is fully effective but that is true of other drugs like methotrexate as well. If you read the side effects of aspirin you would never take it even though it has been one, if not the best, most useful drugs ever. All of the suppression meds have lots of side effects but many people tolerate them well. I have been on pred for almost 6 years (almost off now) and the only bad side effect was hypertension which did not occur until after almost a year. The goal of most treatments is to find some prednisone sparing drug like imuran that has less side effects and is tolerated better for long term treatment.
MCTD (lupus, scleroderma, polymyositis). Diagnosed 2005. Kidney, liver, GI tract, dysphagia, raynauds, Barretts esophagus, quadriplegic in 2005. Recovered and now active in skiing, tai, chi, hiking, golf. Meds: prednisone 2.5mg, imuran 25mg, amlodipine, benazapril, omeprazole, potassium, folic acid, vitamins, maxide and various supplements and vitamins.
Remain optimistic and you can overcome the odds.