Hi it may not be related however I would get my thyroid checked if I were you. Hairloss can happen with too much or not enough of thyroid meds
Good luck
It could be a couple of things.
Each different dosage tablet has different fillers or binders, including dyes. You might be allergic to or sensitive to what's in the 25 mcg tablet. Are you taking Synthroid? The 50 mcg tablet is the one without dyes.
Why were you told to take half a dose? Do you have the labs that brought about that decision to post? If so, please do and include reference ranges (they vary lab to lab and have to be posted with results). The decrease might not have been appropriate.
How long have you been on 25 mcg altogether (including the tablets you halved and the new script)?