Thyroid meds are odd compared to many other drugs. Natural products like Armour contain both T4 and T3. T3 is the stuff your body actually uses, but most (emphasize MOST) people convert T4 to T3 as needed. Some do not. Synthetic drugs usually contain only T4 (like Synthroid, Levoxyl, Levothroid, etc.). Cytomel is also synthetic and contains only T3 - it is not sold as a generic, so is more expensive than generic T4. I posted a long time ago (title Thyroid Research) the study that the company that makes Synthroid fought publication of for 10 (ten!) years that shows all brands of synthetic T4 are equally bioactive. It helps not to change brands because the fillers and binders are not quite the same.

It is most important to have the proper tests - Free T3 and Free T4 tell you what is actually circulating in your blood stream. TSH (thryoid stimulating hormone) is produced by the pituitary gland, not the thyroid, and most dr.s only look at it. There is also controversy about which range of numbers is best to use.

Synthetic T4 is usually proscribed in dosages from 75 to 200 micrograms (mcg. - also written .075 to .200 milligrams). Synthetic T3 is prescribe in dosages of 5 to 25 micrograms.

One other thing to keep in mind is that T4 hangs out in the body for 24 to 48 hours, while T3 is only present for 6 to 8 hours after taking it.

I am currently taking 175 mcg of Levothroid (generic T4) and 15 mcg of Cytomel (T3). I take the T4 in one dose as soon as I get up, along with 10 mcg of the Cytomel. I take the other 5 mcg around 6 hours later and find that I don't get as tired in the afternoons and sleep better than when I took the Cytomel in two doses 12 hours apart.

Also, if your low carb diet contains lots of soy protein, you are shooting yourself in the foot because unfermented soy interferes dramatically with thyroid production, conversion and absorption.

Good luck in your quest for better health.