My dh , not on atkins, is hypothyroid and he swears synthroid(synthetic) is very bad.I think the fda just approved it last year. It went all that time without being approved. We went to the about.com thyroid site and found a holistic doctor (they have a list of top docs for thyroid) that prescribed him armour thyroid( Natural) medicine(treats t-3 & 4). He loves it and has been on it for a few yrs now. The regular doctors will not prescribe it , the drug companies give kickbacks for them pushing their drugs. Well, anyway, maybe the medicine has something to do with you being tired this late in the game. At the very beginning I was tired ,but that went away after I began taking my supplements .and that was like week 3 .