After beginning treatment with Synthroid (levothyroxine), you may notice symptom improvement in one to two weeks. However, it sometimes takes several weeks to notice an improvement.
If you are taking Synthroid for an underactive thyroid, you will probably notice that you feel less tired as the drug starts to take effect.
After beginning treatment with Synthroid (levothyroxine), you may
notice symptom improvement in one to two weeks. However, it
sometimes takes several weeks to notice an improvement. If you are
taking Synthroid for an underactive thyroid, you will...
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Stacy Wiegman answered:After beginning treatment with Synthroid (levothyroxine), you may notice symptom improvement in one to two weeks. However, it sometimes takes several weeks to notice an improvement.