Compare Synthroid vs. Armour Thyroid

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

Replaces thyroid hormones.

Synthroid (levothyroxine) effectively replaces thyroid hormone when your body is not making enough, but it's important to take it exactly as instructed since it's affected by other medicines or supplements.

4.1/ 5 average rating with 1090 reviewsforSynthroid
Replaces thyroid hormones.

Armour Thyroid (thyroid desiccated) can be used to treat low thyroid hormone for some people, but it's not the first-choice treatment for this condition.

  • Works well to improve symptoms of an underactive thyroid by supplying thyroid hormone.
  • Unlike some alternative supplements, Synthroid (levothyroxine) is safe to use for any age range and during pregnancy.
  • Compared to some alternative thyroid supplements, Synthroid (levothyroxine) provides a consistent amount of thyroid hormone per pill. Inconsistent amounts can be dangerous.
  • Generic versions are available.
  • Only need to take once a day.
  • Armour Thyroid (thyroid desiccated) is derived from an animal source (pigs), so it's considered natural.
  • Available in cheaper generic form.
  • Even though Armour Thyroid (thyroid desiccated) isn't a first choice recommendation, some people feel better on this medicine compared to other thyroid hormone medications.
  • Synthroid (levothyroxine) must be taken a specific way, separated from some other medicines.
  • Synthroid (levothyroxine) is only T4 thyroid hormone, which is less active than T3 hormone. It may not work for everyone.
  • Initially, your dose may be changing, until you get to the right dose that supplies the right amount of thyroid hormone.
  • Routine blood tests are needed periodically.
  • It can take 6 to 8 weeks to see the full effects.
  • Armour Thyroid (thyroid desiccated) is not recommended by doctors and the American Thyroid Association because of the inconsistent amounts of thyroid hormone in each tablet and the lack of research studies.
  • FDA does not approve Armour Thyroid (thyroid desiccated); they have not found this medicine to be safe and effective.
  • Not recommended for elderly people.
Used for
Dosage forms
  • Pill
  • Pill
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Side effects
The Synthroid (levothyroxine) FDA package insert doesn’t have numbers about how common side effects are.
The Armour Thyroid (thyroid desiccated) FDA package insert doesn’t have numbers about how common side effects are.
Risks and risk factors
  • Weight reduction
    • Taking other medicines for weight loss
  • Heart problems
    • Current heart disease
    • Age 65 or older
    • Taking Synthroid (levothyroxine) with certain types of stimulant medicines
  • Diabetes control
  • Achieving desired thyroid levels
  • Bone effects
    • Duration of treatment
    • Postmenopausal women
  • Adrenal crisis
    • Adrenal insufficiency
See more detailed risks and warnings
  • Overdose of thyroid hormone
    • Taking other drugs for weight loss
  • Changes in blood sugar
    • Diabetes
  • Changes in blood clotting
    • Taking blood thinners
  • Risk of contamination
  • Increased risk of heart problems
    • Angina
    • Elderly
See more detailed risks and warnings