Both Armour Thyroid and Synthroid are brand-name medications used to treat an underactive thyroid gland (hypothyroidism). They belong to the thyroid hormone drug class and work by supplementing thyroid hormones that are usually produced by the body. Hypothyroidism is a common endocrine problem and requires lifelong treatment with thyroid hormone pills. Untreated hypothyroidism is associated with a wide variety of symptoms, many of which are nonspecific. In particular, memory problems and depression (psychometric problems) as well as weight gain are very common symptoms in hypothyroidism but also have multiple other nonthyroidal causes as well.
What are Armour Thyroid and Synthroid?
Armour Thyroid is a natural form of thyroid hormone made from the dried thyroid glands of pigs (desiccated thyroid extract). It contains both T4 and T3 in a fixed ratio. One grain contains around 38 micrograms of T4 and 9 micrograms of T3. Grains can be taken in multiples or fractions. Desiccated thyroid extract also contains unmeasured amounts of calcitonin, diiodothyronine (T2) and monoiodothyronine (T1).
Synthroid, on the other hand, is a brand of levothyroxine, a synthetic form of the T4 thyroid hormone. It contains only synthetic T4, which is biologically identical to the T4 produced by the body. Your body converts some T4 to the active hormone T3 as needed.
Conditions Treated
Both Armour Thyroid and Synthroid are effective thyroid medications. They both replace thyroid hormones in patients whose thyroids do not secrete enough hormones naturally. “Any patient who needs thyroid replacement hormone (because the thyroid is not secreting enough hormone naturally) can potentially benefit from Armour Thyroid or Synthroid,” Dr. Offutt says.
Hashimoto thyroiditis is an autoimmune disease in which the body attacks its thyroid cells. “Either of these medications may be used to treat patients with hypothyroidism secondary to Hashimoto thyroiditis,” Dr. Offutt says.
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How They Work
Synthroid only has the T4 component of thyroid hormone. However, Dr. Offutt says it is believed that humans can convert some T4 to T3 after ingesting it. Levothyroxine is the main thyroid hormone produced by the thyroid gland and the synthetic form is the most common form of thyroid hormone replacement therapy. T4-only replacement (levothyroxine) provides a steady supply of the hormone your body usually makes and lets your tissues convert the amount of T3 they need.
Armour Thyroid (desiccated thyroid extract) delivers some active T3 right away, which can produce peaks and troughs in T3 levels after a dose because T3 has a shorter half-life. For some patients this feels better; for others it leads to fluctuations or symptoms of excess thyroid hormone.
Why the Shift from Armour Thyroid to Synthroid?
Prior to the availability of the pure levothyroxine, desiccated animal thyroid extract was the only treatment for hypothyroidism. As a result, the dosage was often too high and serious side effects were often reported. Conversely, Synthroid (levothyroxine) was thought to offer a safe and consistent dosage.
The following discoveries further solidified the shift towards Synthroid:
- The discovery that most T3 was converted from T4 via an enzyme in the body.
- The diagnostic tools for measuring blood levels of thyroid hormones advanced.
Dosage and Administration
Synthroid is prescribed in tablets that range from 25 to 300 mcg in strength and is usually taken once a day with a full glass of water (about 8 ounces) 30 to 60 minutes before breakfast for best adsorption into the body. Children can take the medicine if the tablet is crushed and put into about 1 to 2 teaspoons of water; do not store or delay giving this crushed pill suspension. Doctors often may have to slowly increase the dose; patients should not increase or decrease this medication themselves. Because some preparations of the drug may contain iodine or lactose, patients should tell their doctors about such allergies or reactions to these components. Many drugs can inhibit Synthroid's adsorption by the body; other medications may increase or decrease its effectiveness once it is adsorbed. Providing a complete list of medications to the doctor will help with getting the correct dose established for each individual patient.
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The dosage of Armour Thyroid is determined by the condition being treated and is individualized according to patient response and laboratory findings.
Side Effects
Adverse reactions of both Armour Thyroid and Synthroid tend to be symptoms of thyroid problems rather than drug side effects. Common symptoms of imbalanced thyroid hormone include weight changes, hair loss, fast heart rate, and excessive sweating or nervousness. Side effects of Synthroid and Armour Thyroid are somewhat similar, with the exception of fatigue.
Drug Interactions
Drug interactions with Synthroid and Armour Thyroid tend to result in decreased thyroid hormone absorption. According to an observational study that included 10,999 patients, the most common drug interactions with Synthroid (levothyroxine) are iron, calcium, proton pump inhibitors, statins, and estrogens. These medications increase thyroid stimulating hormone (TSH), which helps regulate hormones made by the thyroid, in patients taking levothyroxine.
Armour Thyroid may interact with birth control pills or hormone replacement therapy, blood thinners, insulin or oral diabetes medication, medications that contain iodine, salicylates such as aspirin and others, or steroids. Tell your doctor all medications you use.
Warnings
Synthroid and Armour Thyroid both have an FDA boxed warning (once known as a black box warning) advising against taking them for weight loss. Even when taken to supplement thyroid hormone levels, there are still serious possible side effects to be aware of. Severe diarrhea and intense sweating should be reported to a healthcare provider immediately. These are signs of hyperthyroidism-too much thyroid hormone due to overdosage. Also, let your healthcare provider know if you are pregnant or breastfeeding.
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Current information shows Armour Thyroid may be used during pregnancy. Tell your doctor if you are pregnant because your dose may need to be adjusted. Thyroid hormone passes into breast milk but is unlikely to harm a nursing infant. Consult your doctor before breast-feeding.
Cost and Coverage
Armour Thyroid costs more than Synthroid, according to Dr. Offutt. Without insurance, Armour Thyroid costs about $55 for 30, 60 mg tablets, while Synthroid costs about $76 for 30, 100 mcg tablets. However, drug prices vary widely. SingleCare coupons can help you save on Armour Thyroid, bringing the cost down to about $28 for 30, 60 mg tablets.
Evidence for Synthroid Over Armour Thyroid
Current thyroid association guidelines recommend Synthroid as the first treatment option. Levothyroxine (Synthroid and generics) is the evidence-based, standard treatment for hypothyroidism because it offers predictable dosing and safer, easier monitoring.
Essentially, T3 given in medication (Armour Thyroid) makes regulating blood T3 levels difficult. Synthroid produces more consistent hormone levels and fewer side effects.
Do Some People Feel Better on Armour Thyroid?
Some patients who continue to have symptoms of hypothyroidism when taking levothyroxine report improvement in these symptoms when switched to desiccated thyroid extract. Some patients still prefer or feel better on desiccated thyroid extract like Armour Thyroid, and clinical trials show a meaningful minority do prefer DTE.
In a double-blinded study of 70 participants, those taking Armour Thyroid lost nearly three pounds more than those taking Synthroid. It’s possible a small percentage of people feel better with Armour Thyroid because of the T3 component. Some people with specific genetic mutations may not be able to either convert T4 into T3 or transport T3 in and out of cells from the blood.
A minority of people may not find symptom relief with Synthroid. A minority report feeling better on DTE or on combination therapy (T4 plus synthetic T3 given under close medical supervision). Because research is mixed and risks exist, switching should be a shared decision made with an endocrinologist or experienced prescriber.
Is Armour Thyroid Better Because It’s Natural?
Synthetic thyroid hormones are biologically identical to animal hormones and will produce the same effects.
Armour Thyroid and Weight Loss
Although weight loss can be a side effect of Armour Thyroid in people taking it for low thyroid levels you should not take Armour Thyroid for the sole purpose of losing weight. Using Armour Thyroid to reduce weight in people with normal thyroid levels is dangerous, not safe, and can be life-threatening. Strokes, seizures, shock, coma, and death have been reported in people who have taken higher than recommended dosages of thyroid hormone preparations for weight loss. Some symptoms of Armour Thyroid toxicity (overdose), such as confusion, disorientation, sleep disturbances, or heart changes may not appear until several days after ingestion.
Armour Thyroid should not be used as a treatment for weight loss or obesity. Weight gain is an uncommon side effect of Armour Thyroid but may occur if the dosage of Armour Thyroid is not supplementing their low thyroid levels enough. High blood pressure is not a common side effect of Armour Thyroid but it may occur if too much Armour Thyroid is taken. High blood pressure can also occur a result of low thyroid levels (hypothyroidism) and this may persist despite treatment with Armour Thyroid. Do not increase your dosage of Armour Thyroid without your doctor telling you to do so because too much Armour Thyroid is not safe. Losing weight can often help bring thyroid hormone levels back to normal.
Potential Drawbacks of Armour Thyroid
- Inconsistent dosage: There may still be inconsistencies and stability problems in the preparation of Armour Thyroid.
- Difficulties maintaining T3 levels: The ratio of T4 to T3 in Armour Thyroid is much higher than that typically excreted from a healthy human thyroid. T3 levels may spike or become elevated and symptoms such as heart palpitations and others seen in hyperthyroidism can occur.
Considerations for Specific Patients
- Pregnancy and children: Levothyroxine is generally preferred because maintaining stable T4 is critical for fetal brain development and precise dosing and monitoring are easier. If you try DTE or T3-containing regimens, monitor closely.
- Hypothyroidism associated with thyroid surgery, cancer or pregnancy may require a different treatment plan.