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Compare Synthroid vs. Armour Thyroid

Head-to-head comparisons of medication uses, side effects, warnings, and more.

Key takeaways

Synthroid (levothyroxine) and Armour Thyroid (desiccated thyroid) are both used to treat low thyroid hormone levels, but they have some key differences. Synthroid is a synthetic (man-made) version of the T4 thyroid hormone, while Armour Thyroid is a natural product derived from pigs and contains both T3 and T4 hormones. Synthroid is typically the first-choice treatment because it has consistent hormone levels and is FDA-approved, whereas Armour Thyroid can have varying hormone levels between batches and is not traditionally FDA-approved. Both medications are taken once daily on an empty stomach and have many interactions with food and other medications. Side effects for both are rare and usually related to taking too much, but Synthroid can take 4 to 6 weeks to show full effects, whereas Armour Thyroid typically takes about 2 to 3 weeks. If you haven't had success with Synthroid, your healthcare provider might consider switching you to Armour Thyroid.

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