There can be side effects from the HU similar to what you mention, especially when the dosage is higher. The older we get the more difficult it is sometimes for bodies to process the meds. Water can definitely help to flush the meds through the system.

As mentioned by @nohrt4me, some people have difficulty tolerating HU and will start out on lower dosages, working their way to a higher amount. Though your mom’s stomach upset seems to have developed with the increased dosage. This will be a good subject to discuss with her doctor so, together, they can find a treatment that works for her with minimal side effects.

Since her numbers went up while taking HU it might be a good idea to check in with a specialist who works with blood conditions to find the root cause of her increasing platelets. Is she seeing a hematologist for this diagnosis?

Your mom should try taking the hydrea with a meal (I don't take it at night because I have digestive issues as well) and drink at least 60 ounces of water every day. The water helps to flush the medicine through her system and to keep her hydrated.