What is this T3 stuff?

[Itsjakefromstatefarm]

So I got armour from the doctor..should I be on t3 only? How will I know?

[humanbean]

Levothyroxine is T4 only. When it is taken it gets converted to T3 or Reverse T3 by removing one of the iodine atoms from T4.

T4 is a pro-hormone - it has little or no activity itself, it just acts as a storage hormone for the body to make T3 when needed.

T3 is the active hormone and is the one that makes people feel well or ill, depending on levels.

NDT contains T4 and T3.

Taking T3 only can be difficult and really is a last resort. You are always skating on thin ice with T3 only, because you are unlikely to have any stores of T4, so theoretically you could find yourself with no thyroid hormone in your body very quickly in the event of an accident (for example).

Taking enough T3 to keep you healthy will mean that the body decides that little or no T4 is needed. When I was on T3 only I had one test where my Free T4 result was 1.94 pmol/L (12 - 22). I actually felt reasonably well at the time.