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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.

  • Synthroid (levothyroxine)
    Armour thyroid (desiccated thyroid)
  • Synthroid (levothyroxine)
    Armour thyroid (desiccated thyroid)

  • Summary of Synthroid vs. Armour Thyroid

    Summary for Thyroxine (T4)
    Prescription only

    Synthroid (levothyroxine) is a thyroid hormone used to treat low thyroid hormone levels (hypothyroidism) in both children and adults. It's also used to treat a certain type of thyroid cancer. The medication comes as tablets in many different strengths. It's taken once a day by mouth, usually on an empty stomach in the morning. You'll need regular blood tests to make sure you're getting the right dose. Side effects can include headache, trouble sleeping, and weight loss.

    Summary for Thyroid hormone replacement (T3 / T4)
    Prescription only

    Armour Thyroid (desiccated thyroid) is a prescription medication used to treat hypothyroidism and other various thyroid-related health concerns for children and adults. It works by bringing your low thyroid hormone levels back up to normal. The active ingredients come from an animal source, so it might be a good choice if you're looking for a natural thyroid replacement. You typically take a dose by mouth just once daily, and side effects are rare unless you take too much of it.

  • Indications of Synthroid vs. Armour Thyroid

    Indications for
    •Hypothyroidism (low thyroid hormone levels)
    •Thyroid cancer, together with radioactive iodine and surgery
    Indications for
    •Hypothyroidism (low thyroid hormone)
    •Lowering thyroid-stimulating hormone (TSH) levels in people with other thyroid problems like goiters or thyroid cancer

  • Pros and Cons of Synthroid vs. Armour Thyroid

    Pros and Const for Thyroxine (T4)
    Pros
    •First-choice medication for treating low thyroid hormone levels
    •Safe to use during pregnancy
    •Only needs to be taken once a day
    •Can be taken by both children and adults
    Cons
    •Must be taken on an empty stomach
    •Might take several weeks to find the right dose
    •Requires regular blood tests
    •Interacts with many foods, medications, and supplements
    Pros and Const for Thyroid hormone replacement (T3 / T4)
    Pros
    •Natural thyroid hormone derived from an animal source
    •Taken once daily by mouth
    •Might help when other thyroid medications haven't worked well
    •Available in multiple strengths
    Cons
    •Amount of thyroid hormones can vary between batches of medication
    •Must separate from food and other medications
    •People with serious heart problems might require more careful dosing
    •Not traditionally approved by the FDA

  • Common Side Effects of Synthroid vs. Armour Thyroid

    Common Side Effects for

    Signs of having too much thyroid hormones in the body, such as:

    •Irregular heartbeat
    •Chest pain
    •Shortness of breath
    •Leg cramps
    •Headache
    •Nervousness
    •Hives or skin rash
    •Irritability
    •Trouble sleeping
    •Tremors
    •Muscle weakness
    •Change in appetite
    •Weight loss
    •Vomiting
    •Diarrhea
    •Sweating a lot
    •Sensitivity to heat
    •Fever
    •Changes in menstrual period
    Common Side Effects for
    •Signs of having too much thyroid hormones in the body:
    •Nervousness
    •Irritability
    •Tiredness
    •Muscle weakness
    •Trouble tolerating heat
    •Trouble sleeping
    •Shaky hands
    •Fast heartbeat
    •Diarrhea
    •Weight loss
    •Mood swings

  • Warnings of Synthroid vs. Armour Thyroid

    Common Side Effects for
    •Not for weight loss
    •Heart problems
    •Adrenal crisis in people with adrenal insufficiency
    •Worsening diabetes
    •Bone loss
    Common Side Effects for
    •Not for weight loss
    •Dangerously low stress hormone levels (adrenal crisis)
    •Worsening diabetes
    •Risk of heart problems
    •Interactions with other medications

  • Prices with our coupons for Synthroid vs. Armour Thyroid

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