Liz1967
You still have a thyroid which could at any time randomly chug out more hormone, or less, overriding the dampening effect of your medication. Remember your thyroid is diseased and under attack from antibodies, which will continue to be active as long as they have something to attack. When you have no thyroid, as via thyroidectomy, you are producing no hormone so there can be no variation, no swinging between too much and too little. You take levothyroxine and what goes in is what you have, no surprises. There is one less organ to rile up the antibodies, although they do attack eye muscles too. Regulating by TSH is easiest and on PTU, you have to rely on free Ts for dosing. And after all is said and done, many people on methimazole etc end up having to take levothyroxine anyway.