I've been on HU since mid-November when I was diagnosed with Essential Thrombocytosis. Started off at 500 mg twice a day, 7 days a week and am now taking it 4 days a week. My platelets were at 792 and are now around 200. I have been fortunate that my side effects have been mild - while on the 7 day-a-week regimen I got sudden, severe headaches that lasted less than 30 seconds. This didn't happen often enough to concern me, and they stopped when my dosage regimen was changed. Given the reduction in my platelet counts, I am happy to stay on HU for the foreseeable future.