How long after mixing up thyroid meds that aided hair to fall our due to the change will it correct itself?

You have to : Really mess up your thyroid meds for a long time to cause hair loss. Unless due to a toxin like chemotherapy or hair dye, hair loss is usually the result of something that happened many months ago. It will then take many months to grow back out, but it will normalize if it was due to thyroid and your thyroid level is back to normal and kept at normal.