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

Most common
Headache (not quantified)
Palpitations (not quantified)
Insomnia (not quantified)
Tremor (not quantified)

Armour Thyroid

Most common
Headache (not quantified)
Palpitations (not quantified)
Insomnia (not quantified)
Tremor (not quantified)

Synthroid vs. Armour Thyroid Dosage

Synthroid

Dosage
Dosage Table
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

Dosage
Dosage Table
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.