NP Thyroid and Armour Thyroid are not the same medication, but they are very similar. Both are desiccated thyroid extract (DTE) made from pig thyroid glands, and both contain the same two active hormones: T4 (levothyroxine) and T3 (liothyronine). The key differences come down to who makes them, what inactive ingredients hold the tablet together, how much they cost, and their track records for consistent potency.
What the Two Brands Share
Both NP Thyroid and Armour Thyroid are classified as animal-derived thyroid medications. They use porcine (pig) thyroid powder standardized to deliver a fixed ratio of T4 and T3, the same two hormones your own thyroid gland produces. The active ingredient is identical in concept: dried, powdered thyroid tissue processed into tablets at specific strengths.
Both products are available in a wide range of tablet strengths, from 15 mg up to 300 mg, which gives prescribers flexibility to fine-tune dosing. And here’s something many patients don’t realize: neither NP Thyroid nor Armour Thyroid is FDA-approved. The FDA classifies both as “unapproved animal-derived thyroid medications” that have not been formally reviewed for safety, purity, or potency through the standard drug approval process. They remain on the market largely because they’ve been sold for decades and predate modern FDA requirements.
Different Manufacturers, Different Formulations
Armour Thyroid is made by AbbVie (formerly Forest Pharmaceuticals), a large pharmaceutical company with a long history of producing this brand. NP Thyroid is manufactured by Acella Pharmaceuticals, a smaller company. While the active thyroid powder is functionally the same, the inactive ingredients differ between brands.
Inactive ingredients are the fillers, binders, and coatings that hold a tablet together and affect how it dissolves in your body. These differences matter more than many people expect. Some patients report feeling better on one brand versus the other, and the most likely explanation is that different fillers change how quickly or completely the thyroid hormones are absorbed. Patients with sensitivities to specific ingredients like certain dyes, lactose, or corn-derived compounds may tolerate one brand better.
Because these are not FDA-approved products, the FDA does not rate them as bioequivalent or interchangeable. There’s no official “AB rating” in the FDA’s Orange Book confirming that switching between the two will produce identical blood levels of thyroid hormone. In practice, this means your doctor may want to recheck your thyroid levels if you switch from one to the other.
NP Thyroid’s Recall History
One of the most significant practical differences between the two brands is NP Thyroid’s potency recall. In April 2021, Acella Pharmaceuticals issued a voluntary nationwide recall covering multiple lots of NP Thyroid in the 15 mg, 30 mg, 60 mg, 90 mg, and 120 mg strengths. Routine testing found that the recalled tablets contained less than 90% of the labeled amount of T3 and/or T4. In plain terms, patients taking those lots were getting meaningfully less thyroid hormone than they thought.
Sub-potent thyroid medication can cause a return of hypothyroid symptoms: fatigue, weight gain, brain fog, cold sensitivity, and depression. For patients who had been stable on NP Thyroid and suddenly felt worse, the recall explained what happened. This wasn’t NP Thyroid’s first potency issue either, which has made some patients and prescribers more cautious about the brand. Armour Thyroid has had a more stable manufacturing track record by comparison, though no medication is immune to production variability.
Price Differences
NP Thyroid is generally the cheaper option. Without insurance, 100 tablets of NP Thyroid 30 mg run about $81 (roughly $0.81 per tablet), while 100 tablets of Armour Thyroid 120 mg cost around $219 ($2.19 per tablet). Even accounting for the difference in strength, NP Thyroid tends to cost less at equivalent doses. For patients paying out of pocket, this gap is substantial over months or years of daily use.
Insurance coverage for both brands varies widely. Because neither is FDA-approved, some insurance plans don’t cover either one, or they place them on higher cost-sharing tiers. If your plan does cover one but not the other, that alone may determine which brand you end up on.
Does Switching Between Them Matter?
Because the active thyroid powder comes from the same animal source and follows the same USP (United States Pharmacopeia) standards for hormone content, many patients switch between NP Thyroid and Armour Thyroid without major issues. But “without major issues” isn’t the same as “no difference at all.” The different inactive ingredients can subtly change absorption, and thyroid hormone replacement is one of those areas where small shifts in blood levels produce noticeable symptoms.
If you’re switching brands for any reason, whether cost, availability, or a recall, it’s reasonable to have your thyroid levels rechecked about six weeks after the change. That’s roughly how long it takes for your body to reach a new steady state on thyroid medication. You’re looking for any shift in your TSH, free T4, or free T3 that might call for a dose adjustment.
Some patients find they strongly prefer one brand and feel noticeably different on the other. This isn’t imagined. Individual differences in gut absorption, sensitivity to fillers, and even the rate at which a tablet dissolves can all play a role. If you’ve been stable and feeling well on one brand, there’s no medical reason to switch just because the other exists.
Why Both Remain Unapproved
The FDA has publicly stated concerns about the safety and effectiveness of all animal-derived thyroid medications, including both NP Thyroid and Armour Thyroid. The core issue is that these products were never put through the rigorous clinical trials that modern FDA approval requires. They’ve persisted on the market through a regulatory gray area, grandfathered in by decades of use.
This doesn’t mean they don’t work. Millions of patients take desiccated thyroid and do well on it, and some prefer it over synthetic alternatives because it provides both T4 and T3 rather than T4 alone. But the unapproved status does mean there’s less regulatory oversight of manufacturing consistency, which is exactly the kind of gap that led to NP Thyroid’s potency recall. If you’re taking either brand, paying attention to how you feel and staying current on thyroid blood work is your best safeguard against batch-to-batch variability.