I was on HU for 24 years. Only side affect was fatigue and yes- thinning hair.
Then I developed a bad case of locally advanced skin cancer on my head. As you know, on HU, you are sensitive to the sun and should be diligent with sunscreen all year round. But who put sunscreen on their head? I didn’t.
I was able to control it with a topical cream that took 6 months to eradicate it but I scared me off of HU. Please all- use sunscreen.

I am now on Anagrelide. I had no previous heart issues so it works for me.
Yes, it initially gave me some heart palpitations but my body adjusted.
I also take nicotinimide which works to thicken my hair and has been shown to be helpful in keeping skin cancer at bay. I am 66.
Was diagnosed with ET at 39.