Hi Eileen, I have been on Pegasus for 7 weeks, at a dosage of 45 mcg weekly. Last week I had my blood drawn and my platelets came down from 588 to 320, into the normal range. Unfortunately my white blood cells are now a little less than normal. I am going to continue this dosage for another month and have another blood draw. I have really not experienced any side effects from the drug up to this point. I have had ET for 30 years, but only recently found out I had JAK2, so I accepted that I needed to do something. Best of luck to you.