I take 100mcg thyroxine and was okay on it for 3 years. Since having my second child I've become very light-headed and dizzy and am going onto adrenal supplements, NUTRI thyro-complex and selenium to see if that will all help me generally to get what I need out of the T4. However at the moment I am taking antibiotics for an infection and they seem to completely wipe me out. It has occurred to me that they are wiping out both my meds and my own thyroid action, so today I took another 100mcg this afternoon at 2pm. I felt really good til about 6pm, then light-headedness returned. I've got 5 more days of antibiotics. If an extra dose of thyroxine lasted me 4 hours today, I recon I would need 2 extra doses tomorrow. Partly I think, this is fine. With a lot of the reading I am doing at the moment, it seems that I should learn to self-dose a bit according to symptoms and that normal thyroid function would naturally vary according to extra stresses, so maybe this is just what I need to do to counteract the antibiotics? Any thoughts welcome. Thank you!!