As much as I wanted it to work, sadly, it didn't. I had been on Synthroid for 5-6 years, based on high TSH (50's). I had very few symptoms and they never tested anything but TSH and T4. The Synthroid didn't help me, I thought, as I got fatter, on more meds, etc... After I started paleo eating in Jan 2011, I quickly lost 50lbs and got off all meds. In May 2011, i started halfing my 150mcg Synthroid pills. TSH stayed very low for several months (.55). I quit altogether in Sep. In Oct my TSH was 1.5, T4 mid-range. In Nov I noticed my toes getting cold in a warm house and my weight loss completely stalled. In Dec my TSH was 2.5, T4 lower mid-range, toes cold, weight stalled. 5 Jan 2012 I requested full thyroid panel: TSH was 4.2, T4 below range, T3 at bottom of range, no thyroid antibodies present. They didn't check rT3, but I assume it would be non-existant since i had no T4.
I restarted my Synthroid on 10 Jan and have an Endo appt at end of this month. I hope to get a rx for a natural dessicated thyroid (Armour or equiv).
I started supplementing with selenium and iodine (kelp tabs) in December, wish I had started years ago.
What it seems to me is my thyroid is indeed not working well. The Sythroid must have accumulated in my body and it took 3 months to run it out. I have heard that T4 has a long life and T3 an extremely short (6 hours).
Bottom line, if you quit, be sure to test. Hypothyroidism is a bitch and without proper levels you are hosed as far as weight loss and health long term.
I really don't know why I am so against taking Sythroid--if it was sold as a supplement, I'd probably brag about taking it, like my Vit D 10,000IU/day.
Post back and let us know how you make out. I will do the same.