I have Giant Cell Arteritis and ordered melatonin to help me sleep as the high dosage of prednisone I was on made sleep difficult. All melatonin bottles have warnings not to take if you have an autoimmune disorder, which both PMR and GCA are. I'm glad I read that before taking the melatonin. If I recall correctly, melatonin stimulates the immune system, but as both PMR and GCA are autoimmune disorders - with genetic markers -we want to calm down ou immune systems (with Prednisone), not overstimulate them. I had success sleeping better with lemon balm tea, and now that I'm on a lower dose of prednisone, 4 mg, I sleep fine. All the best, Teri