I've taken sulfasalazine before for RA. One of the drugs I had to "fail" before moving on to the biologics. Sulfasalazine, as someone already pointed out, commonly causes allergic reactions in certain populations. After about
4-5 weeks on the drug, my blood counts plummeted and I developed petichiae (sp) all over my body. It was only the prednisone I received from an ER doctor that brought my platelets back up to normal. After that scary experience, I stopped sulfasalazine and was told that I was allergic to sulfa drugs (even though I never was before).
If you are not allergic to sulfasalazine, however, I've heard it can be a very good drug.