I started taking throid meds how fast do they start working?

Depends: It depends on your body, the med & dose, how low your thyroid levels are to start with, etc. Especially if your levels are low, you may start to feel a little better in a couple of weeks. Steady levels are usually reached in 4-6 weeks, which is when your blood levels are usually retested to see if dose needs to be changed. The dose shouldn't be increased too fast as it can cause heart problems.

Onset of thyroid med: The thyroid meds take 5 have lives to equilibrate. The half life of thyroxine (T4) is 7 days. So, once you start on or change your T4 dose, it takes about 35 days to reach a steady state.