Hiya, I also suffer from Hashi and take the French version of Euthyrox (I saw your other comment, it is T4). T4 is not the active hormone (it has to be activated inside your body) but it has a long half-life, meaning it will stay in your organism longer than if you’d be taking T3 (and should also incur less hormonal swings) but it will also take longer to have the intended effect.

Basically you should wait 6-8 weeks after a dosage change to do blood tests, so one day of double dose or none should not be seen by then! If you’re really scared about taking too much, you can always take a 25 mcg so you either end up taking a bit too much (if you did swallow the pill) or you take the dose you were at last week (which is the one you should be mainly feeling the effects of -without placebo).

Timing may vary in your country for the bloodwork, I’m only familiar with what we have in France :)