Aromasin lowers estrogen levels in postmenopausal women with breast cancer (estrogen dependent). It is often given to women whose cancer has progressed even after surgery, radiation, or other cancer medications have been tried without success. The common side effects include: joint pains, body aches, bone pains, hot flashes, etc. It is known to cause osteoporosis ( thinning of the bones) but it does not cause Rheumatoid arthritis. Rheumatoid arthritis is an auto immune disease due to production of antibodies against the articular cartilage and other tissues. It may co-exist but Aromasin is not the causative factor for rheumatoid arthritis. I hope I have clarified your doubts. kindly consult you doctor for the joint pains.