Hi @kapow. While you’re waiting for other members taking hydroxy to Essential thrombocythemia can also impact the spleen, which is in the upper left quadrant of your abdominal area. https://www.verywellhealth.com/splenomegaly-enlarged-speen-4068974

There are an number of members sharing their excperience with Hydroxy in this discussion:

~What are most common side effects when starting HU (Hydroxyurea)?
https://connect.mayoclinic.org/discussion/hu-side-effects/
When you press on the area on your upper left side, just under the rib cage, does it feel tender? Do you feel more full after eating?