I am ET JAK2+ and 79 years old. I too have experienced the sharp, sudden headaches. The first one lasted for hours and since then have subsided to perhaps 5 or 10 minutes and sometimes not at all. They begin within about an hour from taking the HU and are very clearly not from any other cause - the timing is predicable. They do not keep me from any planned activity. I take 500mg a day M-W-F. My platelets have decreased steadily from 647 to 387 inside of 3 months. And my doctor has also made it clear, at least with what they know right now, the HU is for life.