Participants stop all medications for itching 4 weeks before starting the study, but continue to take ursodiol during the 42-week trial. On entering the study, patients are assigned to take either SAMe or placebo tablets twice a day for 12 weeks. While taking the medications, they are followed in the clinic every 2 weeks for the first month and then every 4 weeks to fill out symptoms questionnaires and have a short medical evaluation and blood tests. At the end of 12 weeks, treatment is interrupted for a 2-week "wash-out" period, after which patients begin a 12-week crossover treatment; that is, patients who were taking SAMe are switched to placebo, and those who were taking placebo are switched to SAMe.