I was diagnosed with ET and the JAK2 mutation almost 3 years ago and have been taking HU ever since. The only side effect I had was very brief (30 seconds), intense headaches when going quickly from sitting to standing. That subsided after about a week and since then I have had zero side effects - and my platelets dropped from 792 to right around 200. I take 500 mg 2x a day, Mondays through Thursdays, and always take it with a meal.