Chances of Hydrea side effects are low for most of us due to the low dosage needed to regulate our blood. However, some of us do have negative reactions. Hair loss is NOT a side effect of the medication in the dosage we need, but can be caused by stress and/or is age related (since most of us are upwards of 60). The mouth sores, which are a reported side effect, can be alleviated with proper hydration.