What are most common side effects when starting HU (Hydroxyurea)?

I have taken my Synthroid for years first thing in the morning and always at least an hour before eating. When I started 1000mg of HU about five years ago, hematologist suggested I take the HU at night before bed in order to minimize side effects. She knew I was on Synthroid and never mentioned it in that discussion. I can’t say I’ve ever been nauseous and attributed it to the HU. So, there’s at least an 8 hr gap between HU and Synthroid.

I started Hydroxyurea 7/05/25 500mg daily. Very mild side effects including short episodes of hot flashes, a tiny hint of nausea a few times, and two episodes of fatigue. After napping a few hours I felt much better following g the fatigue. My dose was just increased to 1,000 mg daily due to increased platelets. A bone marrow biopsy is scheduled three days from now.
I am trying to eat very little processed foods, am drinking a lot of water, and jogging in the pool for an hour every day. Hopefully these efforts may be helping to minimize side effects 🤷‍♀️

I also take Synthroid for thyroid every morning around 8:30. I eat a late breakfast and wait until 12:30 to take HU. Have you been told to have 12 hrs between thyroid meds and HU? My sister takes her thyroid meds before bed but she eats an early dinner and likes to eat breakfast immediately and not wait the hour. I guess I might have to rethink my plan also. Main question is how long to wait to take HU after Synthroid? I might have to push it to mid-afternoon. Oncologists don't seem to know this issue so will have to ask endocrinologist.

I take Levothyroxine every morning since I have had a complete thyroidectomy. So HU at night works for me. I'm glad it's working for you to change to AM for HU. It's tricky juggling medications. I may need to try taking HU in the morning and Levo. at night....
Best to you!

I have not been tested for gout, but I am experiencing peripheral neuropathy now and I think it's the Hydroxyurea causing that along the toe jabs.
Thanks for your insight. Isn't that hair loss annoying!
My best to you!

I started HU with a night dose but after 5 weeks decided to change to a morning dose. This change gave me better sleep, vivid dreams gone, less need for using bathroom, not waking up at 5am, and fatigue doesn't hit until bedtime. It's only been a few days since changing to morning dose but it seems worth the change so far.

Have you been tested for gout? My JAK2 was determined after I complained of bad knee pain (and my toes hurt too) and it was gout. Easy fix, allopurinol. I still have pains in my legs and fee at night, but better.
And, my hair brush also tells that story.

Extreme sensitivity to sun, small brown spots on skin, and random tooth pain and that sucks! Feels like nerve pain and your gums feel
Sore constantly. Yes, hair loss but that Les seems over time. Good luck!

The varying side effects are interesting to me. I have them all! I started on HU in March 2025 and my 500mg daily dose has reduced my platelets from 1200 to 370! I HAVE lost hair! Every day my hairbrush has the evidence and it’s way more than ever before! I too have shin bone aches at night, vivid dreams, and extreme fatigue by 2:00 in the afternoon and I’m taking HU at night before bed. Jabbing toe pain is now occasional, but was terrific before HU! I take Aspirin ever other day and bruise spots are showing up. I’m 73, female, have JAK2, TET 2 and ASXl1 mutations.I want to stay hopeful—it’s hard with hair thinning and symptoms that are upsetting! I get it—you’re not alone!

That is why I always ask for, and my doctor wants, even though he is very experienced, my BMB to be CT-guided. It means being out patient in the hospital for 2-3 hours, but he *always* gets the right spot for his blood and marrow samples! (5 times??? Geesh!).