Quote Originally Posted by Triskeliongirl View Post
The half life of T4 (which is what I think you are taking since you said levothyroxine) is 5-7 days. That means that as long as you take it at ~ the same time daily, there should always be a similar constant amount of it in your bloodstream. You should not notice it 'wearing off'. T3 (cytomel) is a little different, its half life is only a day, and I do find if I take it too late in the day I will have trouble sleeping. So I take both my T4 and T3 first thing every morning, and have even energy throughout the day.
Yeah, it's just T4. Huh. I really feel like I can feel it, but I guess it's likely psychosomatic. It may just be another case of where I'd forgotten what normal-me felt like -- this went undiagnosed for quite a while and I just thought that was what turning 30 was supposed to feel like. Or some sort of mild idiosyncratic reaction; my dad swears that as a kid he and his brothers could tell if my grandmother didn't take hers in the morning, and she was (and is) on T4. The crashing at 11pm I can't do much about except try to plow through lots of high-protein food around then, which seems to help; unfortunately that works better for non-athletic all-night efforts than it would on a brevet.

(The trigger for asking is that I'm doing a 200K that starts at 10pm the weekend after next, and I'd like to start doing longer brevets, though that won't happen until next spring as the 300-400Ks around here are all done for the year.)