I'm on synthroid since 1988 since I take a full replacement dose of it after a thyroidectomy. It takes 2-3 weeks for the onset since your body has to break it down from t4 to t3 to use. You won't feel anything from it in all likelihood. I take 150 mcg a day. I've taken pure t3 too, which can give you heart palpitations.

Synthroid is not a bad medication. I have to take it for life. If you are on too much, you will probably feel more awake, hungry, possibly edgy, hot, and have hair loss or rapid growth. You'll just stop taking it if so. It would be gradual, like over six months, in most cases.

Don't take the generic. It doesn't work as well. I have to take a completely different dose on the generic.