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.

http://emedicine.medscape.com/article/819692-overview
Do you think it's possible that the OP's sense of the levothyroxine wearing off is a sign that she could benefit from T3 replacement as well? I'm hyper, not hypo, so I'm not as well versed in hypothyroidism, but from what I've read, some docs are better at others at detecting and treating T4 to T3 conversion problems.

To the OP, when you doc check your thyroid levels, does she/he look at both Free T4 and Free T3 or does she/he look only at TSH? To get a complete picture, I'd make sure you get your Frees checked. If T3 is low relative to T4, I'd discuss T3 replacement therapies with the doctor.