I have been on it for a month now and see my Neph on the 12th. I was on Imuran for my colitis and every time I tried to get off the pred my proteins went up (I did get down to 1). I went to my rhematologist today and he prescribed Cellcept. I wondered how long I have to be on it for it to start working? I seem to be getting worse with pain and the petechiae and my spleen is swollen and other things. Common Questions and Answers about How long does it take cellcept to work cellcept Well, today my Rheumy who has been calling my disease a Mixed Connective Tissue Disease finally told me I have Lupus. Mycophenolate is a disease-modifying anti-rheumatic drug (DMARD) used for lupus and vasculitis. Learn how it works, how long it takes, risks and side-effects. CellCept®180820 5 How long to take CellCept CellCept should be taken every day. It is important to keep taking CellCeptto ensure your transplanted organ keeps working properly. Common Questions and Answers about How long does it take for cellcept to work cellcept Well, today my Rheumy who has been calling my disease a Mixed Connective Tissue Disease finally told me I have Lupus. How long for cellcept to work: I just started cellcept two weeks ago , I have been taking prednisone and mestinon for three years, I'm only taking 15 mg. CellCept (mycophenolate mofetil) weakens your body's immune system, to help keep it from rejecting a transplanted organ such as a kidney. Organ rejection happens when the immune system treats the new organ as an invader and attacks it. I started in October. I increased every two weeks 500 mg twice a day until I was taking 1500mg twice a day. I started feeling weak and tired. My hemoglobin dropped 6.