I don't think the good appetite comes from thyroxine. It is apparently part of being hypo. I also had a huge appetite following surgery, in the weeks before Synthroid was given. I gained 7 pounds in about 2 weeks and have only recently be able to shed 2 of those pounds. A proper dose of Synthroid/thyroxine will not affect appetite but it will help you lose weight since it will increase your metabolism and improve your energy level.