Hi there, I actually had my thyroid removed in February of this year. I started levothyroxin 3 days after surgery. I noticed after taking it I felt jittery and shaky and racing heart, so I didn't take it for a couple days, and was ok. Doc said that was the wrong thing to do.... But... I then had to get my Rx filled through a certain company for insurance reasons, and it was synthroid, I felt a lot better on it and didn't seem to notice those symptoms as much. I then had to have my blood tested again, and they had to increase my dose. So just to quickly go and get my Rx, I went to Wal-Mart and filled it. I noticed the very same symptoms as before (racing heart, jittery, shaky, dizzy, just "weird" feeling). And, I noticed that on the bottle it said levothyroxine again.... So I am not sure what the difference is between them or if there is... but I have noticed differences between the two. THe docs say that I should not notice these changes so fast because it takes awhile to get in your system, but I really believe that I do.