Taken from the hypo forum:

The longstanding protocol for patients whose thyroids have been removed is a combination of T3 and T4 hormones. Doctors surmised that because the thyroid gland is responsible for producing both of these hormones, patients without a thyroid gland would need to have both hormones artificially replaced.

However, the results of a recent study conducted by researchers at the Johns Hopkins Universityâs thyroid clinic found that even after thyroid gland removal, T3 levels often seem to regulate themselves without artificial replacement. In all but a few of the patients studied, post-surgery T3 levels remained stable. In only a few cases was a combination therapy that combined both T3 and T4 hormone replacement truly necessary.

If youâre concerned about finding the right thyroid medication regimen and sticking to it, consult with your doctor for the best insight into your unique health situation. Please check back each week for more of the breaking thyroid news you need!
Link for entire article:
http://www.medicalonly.com/2008/03/08/latest_thyroid_medications