t stay in your system for very long - it peaks within a few hours. Its
half life is only about 1 to 1.5 days. I never really noticed a huge difference when I take it either, but I do notice a difference when I miss more than one dose - of course, I'm now on 10 mcg/day and take it in 2 doses.
If you stop taking it, it would be out of your system within a few days. It could take a bit for your own conversion to ramp up, so you might feel some symptoms before that happens.