Hi @birgitr. Welcome to Mayo Connect. There are several medications which can be used to help people with excess platelet production to keep it under control. HU is one of the frontline medications, been used for decades and fairly well tolerated. Sometimes it can take a little tweaking to find the sweet spot between efficacy and tolerance.
Labs results will show how well the medication is working for you and your doctor will adjust the meds accordingly. If HU isn’t working well your doctor may suggest another option such as interferon based meds.

Since you’re new to the ET diagnosis, it can be helpful to learn a little more about what this blood condition is all about. Here are a couple of links to some informational articles on Essential Thrombocythemia and also on the JAK2 mutation and how that impacts blood cell development and why it’s important to treat it even if you don’t have any noticeable symptoms.
From Very Well Health:
Essential Thrombocythemia
https://www.verywellhealth.com/essential-thrombocythemia-2860907
~What is a JAK2 mutation?
https://www.verywellhealth.com/jak2-mutation-5217909
How long have you been taking the HU? Have labs shown an improvement in the platelet levels?