Armour Thyroid vs Synthroid: What’s the Difference?

When it comes to treating hypothyroidism, two names dominate the conversation: Armour Thyroid and Synthroid. While both aim to restore thyroid hormone levels, their origins, composition, and effectiveness can differ significantly.

What Is Armour Thyroid?

Armour Thyroid belongs to a class of drugs known as Natural Desiccated Thyroid (NDT).These medications are made by drying animal thyroid glands—usually from pigs, sheep, or cows—into a fine powder, which is then pressed into tablets.

Natural desiccated thyroid contains:

• The same hormones found in the human thyroid: T3 and T4.

• Precursors: T2 and T1.

• Additional components: thyroglobulin, vitamins, minerals, proteins, and other substances essential for normal thyroid function.

Main advantage: It’s natural, not man-made, and contains the full range of thyroid hormones and supporting compounds, closely mirroring what the human thyroid produces.

What Is Synthroid?

Synthroid is the brand name for levothyroxine sodium, a synthetic form of the T4 hormone.The name comes from combining synthetic and thyroid.

Here’s the science:

• Natural T4 has the chemical formula C₁₅H₁₁I₄NO₄ — meaning it contains 15 carbon atoms, 11 hydrogen atoms, 4 iodine atoms, 1 nitrogen atom, and 4 oxygen atoms.

• To create Synthroid, one hydrogen atom in T4 is replaced with a sodium atom.

• This modification produces a man-made compound that does not exist naturally.

Why change it?

1. For the pharmaceutical company — the altered molecule is unique, so it can be patented and sold at a higher price than NDT.

2. For patients — although synthetic, it’s structurally close to natural T4, allowing many people to convert it into T3 (the active hormone) and experience benefits.

   
   

Effectiveness: Who Benefits from Synthroid?

• Works well for many: About 70–80% (7–8 out of 10) of patients feel better.

• Does not work for all: 20–30% (2–3 out of 10) see little or no benefit.

Reasons it may not work:

• T4 itself is not active — it must be converted into T3.

• Some people cannot efficiently convert synthetic T4 into active T3.

• In these cases, no matter how much Synthroid is prescribed, symptoms may persist.

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My Clinical Experience

In my practice:

• Patients who felt well on Synthroid stayed with their original doctors.

• I mostly saw patients who did not improve on Synthroid.

Word spread that I prescribed Armour Thyroid, attracting many patients who had no relief from Synthroid.

My approach:

• If a patient was doing well on Synthroid → no change.

• If they weren’t improving (or weren’t on medication despite symptoms because their blood tests were “normal”) → switch to Armour Thyroid.

Results:

• Often remarkable.

• Sometimes took months to find the right dose.

• End goal: patients feeling good and regaining quality of life.

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The Bottom Line

• If Synthroid works for you → stick with it.

• If it doesn’t → consider Armour Thyroid or another NDT.

For those who don’t respond to synthetic T4, switching to a natural, full-spectrum thyroid replacement can make all the difference.

📌 In an upcoming blog, I’ll discuss why many doctors avoid prescribing Armour Thyroid, the misconceptions surrounding it, and the myths that need debunking.