I began taking Nature Throid a week ago. My NP wanted me to start taking it and stop taking my Synthroid (which I've been on for about 8 years now). He also said that if I felt like I was nervous about stopping Synthroid cold turkey, i could half my Synthroid and half my Nature Throid. Well, I went for it by taking only my Nature Throid and after about 4 days was feeling SO hyper! Jittery, shakey, TOTALLY spaced out (major brain fog, more than before I started!) and heart racing. Feels very much like when I had too much Synthroid. I started halving the two today to try to stop this and will call my Dr. tomorrow. Did Nature Throid make any of you Hyper that fast? Wow, it used to take a couple weeks on Synthroid to feel whacky but this was after 3 or 4 days! Whew!