Synthroid vs. Armour Thyroid
See how Synthroid and Armour Thyroid compare on approved uses, dosing, side effects, and cost.
Key Takeaways
Synthroid supplies only T4 hormone, while Armour Thyroid supplies both T4 and T3 from desiccated pig thyroid gland.
Synthroid is FDA-approved through a full New Drug Application, while Armour Thyroid is marketed as a pre-1938 grandfathered drug without that same approval pathway.
Because Armour Thyroid comes from animal glands, its hormone content can vary between batches and it faces more frequent supply shortages than synthetic Synthroid.
Synthroid vs. Armour Thyroid Drug Summary
Synthroid
Synthroid is a synthetic thyroid hormone (levothyroxine sodium, or T4) used to treat hypothyroidism and to suppress TSH in certain thyroid nodules, goiter, and thyroid cancer. It's taken once daily on an empty stomach, with the dose adjusted every few weeks based on TSH levels until stable.
Armour Thyroid
Armour Thyroid is a natural desiccated thyroid hormone from pig thyroid glands, containing both T4 and T3, used to treat hypothyroidism and suppress TSH in certain thyroid nodules, goiter, and thyroid cancer. It's taken once daily, with the dose slowly increased every few weeks until thyroid levels stabilize.
Synthroid vs. Armour Thyroid Side Effects
Synthroid
Armour Thyroid
Synthroid vs. Armour Thyroid Dosage
Synthroid
Armour Thyroid
| STAGE | DOSE | WHEN |
| Starting dose | 1.6-1.7 mcg/kg/day | At the start |
| Maximum dose | 100-125 mcg/day | If needed |
| Dose changes | 3 increases | As tolerated |
| STAGE | DOSE | WHEN |
| Starting dose | 15 mg once daily | At the start |
| Maximum dose | 60-120 mg once daily | If needed |
| Dose changes | 3 increases | As tolerated |
Synthroid
| STAGE | DOSE | WHEN |
| Starting dose | 1.6-1.7 mcg/kg/day | At the start |
| Maximum dose | 100-125 mcg/day | If needed |
| Dose changes | 3 increases | As tolerated |
Armour Thyroid
| STAGE | DOSE | WHEN |
| Starting dose | 15 mg once daily | At the start |
| Maximum dose | 60-120 mg once daily | If needed |
| Dose changes | 3 increases | As tolerated |
Synthroid vs. Armour Thyroid Indications
Synthroid
Synthroid replaces missing thyroid hormone in people with hypothyroidism, whether the cause is the thyroid gland, pituitary, or hypothalamus. It's also used after thyroid cancer surgery or radioiodine treatment to suppress TSH and lower the chance of the cancer returning. It is not approved for weight loss or for fertility problems unrelated to a thyroid disorder.
Primary, secondary, or tertiary hypothyroidism
TSH suppression after thyroid cancer surgery
TSH suppression in thyroid nodules or goiter
Not approved for weight loss
Armour Thyroid
Armour Thyroid also replaces missing thyroid hormone in people with hypothyroidism from thyroid, pituitary, or hypothalamic causes. It's used to suppress TSH in Hashimoto's thyroiditis, multinodular goiter, and thyroid nodules, and as adjunct therapy in thyroid cancer. Like Synthroid, it is not approved for weight loss or for infertility unrelated to hypothyroidism.
Primary, secondary, or tertiary hypothyroidism
TSH suppression in Hashimoto's thyroiditis
TSH suppression in multinodular goiter/nodules
Adjunct therapy in thyroid cancer
Synthroid vs. Armour Thyroid Pros and Cons
Synthroid
Synthroid delivers a precise, consistent dose of T4 because it's manufactured synthetically under FDA-regulated standards, and generic levothyroxine is widely stocked at most pharmacies. Coverage is broad across insurance plans and it rarely faces the kind of shortages seen with animal-derived products.
Pros
Synthetic formulation gives consistent potency batch to batch
Widely available as low-cost generic levothyroxine
Backed by full FDA New Drug Application trial data
Cons
Contains only T4, so some patients still feel symptomatic
Must be taken on an empty stomach, timing matters
Narrow therapeutic index means frequent dose adjustments
Absorption affected by many common foods and medications
Armour Thyroid
Armour Thyroid provides both T4 and T3, which some patients find relieves lingering symptoms that T4-only therapy doesn't fully resolve. Because it isn't FDA-approved through a standard New Drug Application, its safety and efficacy data are less robust, and coverage or availability can be less consistent.
Pros
Contains both T4 and T3, may ease residual symptoms
Derived from natural desiccated thyroid gland, not synthetic
Multiple tablet strengths allow finer dose adjustments
Cons
Not FDA-approved through a standard New Drug Application
Hormone content can vary batch to batch since it's animal-derived
Frequently subject to supply shortages and recalls
Roughly $40 to $155 per month without insurance
Common Symptoms and Related Diseases You Can Explore
Explore a range of common symptoms the Doctronic Symptom Checker can help you understand.