NP Thyroid and levothyroxine are not the same medication. They treat the same condition (hypothyroidism), but they differ in where they come from, what hormones they contain, and how the body processes them. NP Thyroid is derived from pig thyroid glands and contains two thyroid hormones, while levothyroxine is a synthetic, lab-made version of just one.
The Core Difference: One Hormone vs. Two
Your thyroid gland naturally produces two hormones: T4 and T3. T4 is the storage form, and T3 is the active form that your cells actually use. Levothyroxine contains only T4. Your body is expected to convert that T4 into T3 on its own using enzymes in the liver, kidneys, and other tissues. About 80% of the T3 in your body comes from this conversion process, with only 20% coming directly from the thyroid gland itself.
NP Thyroid, by contrast, delivers both hormones at once. Each grain (60 mg) provides 38 mcg of T4 and 9 mcg of T3. That means you’re getting a direct supply of the active hormone rather than relying entirely on your body’s conversion machinery. This is a meaningful distinction for some patients, particularly those whose bodies don’t convert T4 to T3 efficiently. Research suggests that people with very little remaining thyroid function and lower lean body mass may benefit more from receiving both hormones together.
Source: Pig Thyroid vs. Lab-Made
Levothyroxine is entirely synthetic. It’s manufactured in a lab as a precise sodium salt of the T4 molecule. Brand names include Synthroid, Levoxyl, and various generics. Because it’s synthetic, each tablet contains a tightly controlled amount of hormone.
NP Thyroid is a desiccated (dried and powdered) extract of pig thyroid glands. It’s classified as a “natural” thyroid preparation, though “natural” here simply means animal-derived rather than synthesized. Other brands in this category include Armour Thyroid and Nature-Thyroid.
FDA Approval Status
This is one of the most important differences between the two. Levothyroxine has been FDA-approved for decades and is available as both branded and generic medications. NP Thyroid, along with all other animal-derived thyroid products, is not FDA-approved. The FDA classifies these products as biological products under the Public Health Service Act, which also makes them ineligible for compounding. They remain on the market, but without the same regulatory review process that levothyroxine has undergone.
This doesn’t necessarily mean NP Thyroid is unsafe, but it does mean it hasn’t gone through the same standardized testing for potency, purity, and consistency that FDA-approved drugs require.
Dose Conversion Between the Two
If you’re switching from one to the other, the doses are not interchangeable milligram for milligram. NP Thyroid is measured in grains (an older unit of weight), while levothyroxine is measured in micrograms. The approximate conversions, published by NP Thyroid’s manufacturer Acella, look like this:
- 1/4 grain (15 mg) NP Thyroid ≈ 25 mcg levothyroxine
- 1/2 grain (30 mg) ≈ 50 mcg levothyroxine
- 1 grain (60 mg) ≈ 100 to 112 mcg levothyroxine
- 1.5 grains (90 mg) ≈ 150 mcg levothyroxine
- 2 grains (120 mg) ≈ 200 mcg levothyroxine
These are approximations. The T3 component in NP Thyroid makes direct equivalence tricky because T3 is several times more potent than T4 and acts faster in the body. Any switch between these medications requires lab monitoring and dose adjustments.
What Guidelines Recommend
The American Thyroid Association recommends synthetic levothyroxine as the standard, first-line treatment for hypothyroidism. It considers levothyroxine safe and effective for most patients. However, the ATA also acknowledges that desiccated thyroid extract like NP Thyroid is “the treatment of choice for some patients” and supports the principle of personalized therapy. In practice, this means levothyroxine is where most doctors start, but NP Thyroid remains an option, particularly for patients who don’t feel well on T4 alone.
How Lab Monitoring Differs
When you take levothyroxine, your doctor primarily tracks your TSH level and sometimes your free T4. The results are relatively predictable because the medication delivers a steady supply of one hormone that converts gradually.
Monitoring on NP Thyroid is more complex. The T3 component gets absorbed quickly and peaks in the blood within a few hours, which can temporarily push T3 levels above the normal range and suppress TSH more than expected. This doesn’t necessarily mean you’re overmedicated, but it does mean the timing of your blood draw matters more. Drawing blood several hours after taking NP Thyroid can show a very different picture than drawing it right before your next dose. Your provider may need to check free T3 levels in addition to TSH and free T4 to get an accurate reading.
Choosing Between Them
Most people with hypothyroidism do well on levothyroxine alone. Their bodies handle the T4-to-T3 conversion without trouble, and their symptoms resolve. For these patients, there’s no clear advantage to adding T3 through a product like NP Thyroid.
Some patients, though, continue to experience fatigue, brain fog, or weight changes despite having “normal” lab results on levothyroxine. For this group, the addition of T3 (whether through NP Thyroid or a separate synthetic T3 medication) sometimes makes a noticeable difference. The reasons aren’t fully understood, but genetic variations in the enzymes responsible for T4-to-T3 conversion may play a role.
There are also practical considerations. NP Thyroid is an animal product, which matters for people with dietary or religious restrictions around pork. Its lack of FDA approval concerns some patients and providers. On the other hand, some people prefer it precisely because it provides both hormones in a single tablet and because they feel better on it than on levothyroxine alone. Both medications need to be taken on an empty stomach, typically first thing in the morning, and both require regular blood work to ensure proper dosing.