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Drug vs. Drug

NP Thyroid vs. Synthroid: Differences, similarities & side effects

The two drugs work very differently to treat hypothyroidism and thyroid cancer
Karen Berger medical writer and reviewer headshot
By | Jul. 9, 2024
Two round white pills with a "vs." between them: NP Thyroid vs. Synthroid: Differences, similarities & side effects

Key takeaways

  • NP Thyroid and Synthroid are brand-name prescription medications used to treat hypothyroidism (underactive thyroid) or thyroid cancer. Both are available as tablets that are taken by mouth once daily.

  • NP Thyroid contains a mixture of T4 and T3 and is made from pig (porcine) thyroid glands. It is not FDA-approved. Synthroid contains a synthetic form of T4 (levothyroxine) only and is FDA approved. 

  • Clinical guidelines recommend levothyroxine as the main treatment for hypothyroidism and do not recommend products that contain T3.

  • Consult your healthcare provider for professional medical advice on your condition and treatment.

In this article:

The thyroid is a part of the endocrine system and plays an important role in the body’s growth, metabolism, and development. The small, butterfly-shaped gland releases thyroid hormone, which actually consists of two main hormones: thyroxine (T4) and triiodothyronine (T3). While T4 is mostly inactive, T3 is active. When the thyroid releases T4, the body has to convert it into T3 in order to use it. 

NP Thyroid and Synthroid are prescription medications used to treat hypothyroidism (underactive thyroid) and thyroid cancer. Although both medications are therapeutically known as thyroid replacement hormones, they do have notable differences. Continue reading to learn more about both medications.

NP Thyroid vs. Synthroid: Key differences

NP Thyroid and Synthroid are both brand-name drugs. NP thyroid is a natural thyroid medicine that contains both T4 and T3. It comes from the thyroid glands of pigs (the prescribing information notes that the tablet has a strong, characteristic odor) and is dried and ground (known as desiccated thyroid extract, or DTE). Synthroid contains a synthetic form of T4 and is chemically identical to the hormone produced in the human thyroid gland.

Synthroid is also available in a generic formulation called levothyroxine. Both medications come in various doses, as shown in the chart below. These medications can be used in adults and children who are appropriate candidates. 

NP Thyroid vs. Synthroid: Comparing key differences
NP Thyroid Synthroid
Drug class Thyroid replacement hormone (contains both T4 and T3) Thyroid replacement hormone (contains T4 only)
Brand/generic status Brand Brand and generic
What is the generic name? There is no generic available, but the active ingredients are tetraiodothyronine sodium (T4 levothyroxine) and triiodothyronine sodium (T3 liothyronine) Levothyroxine, levothyroxine sodium
What form(s) does the drug come in? Oral tablet: 30 mg (1/2 grain), 60 mg (1 grain),

90 mg (1 1/2 grain), 

120 mg (2 grain) 

 Oral tablet: 25 mcg, 50 mcg, 75 mcg, 88 mcg, 100 mcg, 112 mcg, 125 mcg, 137 mcg, 150 mcg, 175 mcg, 200 mcg, 300 mcg
What is the standard dosage? Varies; dose is individualized and ranges from 15 mg to 180 mg once a day

Tablet is taken once daily, on an empty stomach, with a full glass of water

 Varies; dose is individualized

Tablet is taken once daily, on an empty stomach, 30 to 60 minutes before breakfast, with a full glass of water
How long is the typical treatment? Long-term; lifelong Long-term; lifelong
Who typically uses the medication? Adults and children, including infants (mixing instructions not provided in prescribing information) Adults and children, including infants (for pediatric patients who cannot swallow a pill, the tablet must be crushed and mixed with water, breast milk, or formula since there is no liquid version available)

 

NP Thyroid vs. Synthroid: Conditions treated

People with hypothyroidism, or underactive thyroid, do not make enough thyroid hormone on their own and need replacement thyroid hormone in the form of medication. Hypothyroidism can be diagnosed through bloodwork that measures thyroid function with thyroid stimulating hormone (TSH) levels and free thyroxine (FT4). Measurement of total T4 or T3 levels or FT3 levels is not recommended.

Symptoms of hypothyroidism may include:

  • Tiredness
  • Weight gain
  • Cold intolerance
  • Joint and muscle pain 
  • Dry skin
  • Thinning hair or hair loss
  • Irregular or heavy periods
  • Problems with fertility
  • Slow heart rate
  • Depression 

Both drugs are used to treat hypothyroidism due to various causes, including primary (low thyroid hormone caused by the destruction of the thyroid gland, such as by a condition called Hashimoto’s thyroiditis), secondary (underactive thyroid due to the pituitary gland), or tertiary (underactive thyroid due to the hypothalamus) congenital (inherited) or acquired hypothyroidism. They can also be used to treat certain types of thyroid cancer in combination with other treatments, such as surgery and radioactive iodine.

NP Thyroid vs. Synthroid: Comparing conditions treated
Condition NP Thyroid Synthroid
Hypothyroidism  Yes  Yes 
Thyroid cancer  Yes  Yes 

 

Synthroid vs. NP Thyroid: Which is better?

It is important to note that while Synthroid is approved by the Food and Drug Administration (FDA), NP Thyroid is not. Currently, there are synthetic (made in a lab) versions of thyroid replacement hormones, like Synthroid and its generics, which most hypothyroid patients take. The first versions of thyroid replacement medications, including NP Thyroid, were made from cow or pig thyroid glands and are not FDA approved. 

While FDA-approved medications such as Synthroid undergo extensive clinical testing for safety and efficacy, DTE products like NP Thyroid (or Armour Thyroid, a similar DTE medicine) do not. Some DTE products, such as Nature-Throid and WP Thyroid, have been removed from the market. 

Also, the FDA notes that because Synthroid is consistently manufactured, each tablet contains the exact and correct amount of hormones, which is important in managing thyroid hormone levels. On the other hand, NP Thyroid can vary in hormone levels between batches or even within the same batch. This can result in inconsistent dosing and make patients have symptoms of an underactive or overactive thyroid.

Another factor to consider is that Synthroid contains only T4 (levothyroxine), and NP Thyroid contains a mixture of T3 and T4. In hypothyroidism treatment guidelines, the American Association of Clinical Endocrinologists does not recommend DTE such as NP Thyroid and also notes that there is not enough evidence to recommend a combination of T3/T4, such as NP Thyroid over Synthroid alone. 

Only your healthcare provider can determine which medication is best for you. Consult your provider for more information and medical advice on thyroid replacement therapy.

Can you take NP Thyroid and Synthroid together?

As mentioned above, clinical guidelines do not recommend DTE products at all. Additionally, the guidelines state that experts do not recommend combining products, noting that levothyroxine (the ingredient in Synthroid) alone is the preferred treatment for hypothyroidism. Guidelines note that adding T3 to levothyroxine will not help with hypothyroidism symptoms or affect quality of life. 

NP Thyroid vs. Synthroid: Insurance coverage and cost comparison

A typical out-of-pocket price for NP Thyroid tablets without insurance would be about $60 for a one-month supply of 60 mg tablets. If you use a SingleCare discount card, you can pay as little as $30 per month.

A typical out-of-pocket price for brand-name Synthroid without insurance is about $78 for 30, 50 mcg tablets. However, if you use a free SingleCare discount card, you can pay as little as $4 per month for generic levothyroxine. 

NP Thyroid vs. Synthroid: Comparing insurance & cost
NP Thyroid Synthroid
Typically covered by insurance? Varies  Brand: Varies

Generic: Yes
Typically covered by Medicare Part D? No  Brand: Varies

Generic: Yes
Quantity 30, 60 mg tablets 30, 50 mcg tablets
SingleCare cost* $30 for 30, 60 mg tablets of brand-name NP Thyroid $4 for 30, 50 mcg tablets of generic levothyroxine 
*Cost at time of publication. Drug prices vary by pharmacy.

NP Thyroid vs. Synthroid side effects

Side effects of NP Thyroid and Synthroid are usually caused by a dose that is too high, which causes symptoms of hyperthyroidism (overactive thyroid). These side effects may include:

  • Diarrhea
  • Headache
  • Heart attack
  • Heat intolerance
  • Increased appetite
  • Irregular heartbeat; palpitations
  • Irregular menstrual periods
  • Irritability
  • Muscle spasms or weakness
  • Nervousness
  • Rash
  • Shaking
  • Shortness of breath
  • Trouble sleeping
  • Weight loss

Some individuals will also experience temporary hair loss when starting NP Thyroid or Synthroid.

Keeping your follow-up appointments and getting your blood work on schedule will enable your healthcare provider to prescribe the appropriate dose, which can minimize side effects and keep your thyroid levels in optimal range.

This is not a full list of side effects, and others may occur. Consult your healthcare professional or pharmacist for more information and a full list of side effects. 

NP Thyroid and Synthroid drug interactions

Before you take NP Thyroid or Synthroid, tell your healthcare provider about all the medicines you take, including prescription drugs, over-the-counter medications, vitamins, and supplements. Also, tell your healthcare provider if you take any medicines for your heart, blood pressure, or diabetes. Some people with diabetes will need dosage adjustments on insulin or oral diabetes medicines when starting thyroid replacement therapy. Your healthcare provider will tell you if you need to monitor your blood sugar more frequently.

Certain medicines, vitamins, or supplements, such as iron, antacids, or cholestyramine, must be taken at least four hours before or after you take your thyroid medicine. 

Certain foods and beverages may interact with the absorption of NP Thyroid or Synthroid. This includes soybean flour (found in infant formula), cottonseed meal, walnuts, dietary fiber, and grapefruit, including grapefruit juices. Avoid consuming these ingredients within an hour of taking NP Thyroid or Synthroid.

This is not a full list of interactions. Consult your healthcare professional for more information about drug and food interactions and how they may affect you. 

NP Thyroid vs. Synthroid: Comparing drug interactions
Drug Drug class Interacts with NP Thyroid? Interacts with Synthroid?
Milk of Magnesia

Mylanta

Os-Cal

Rolaids

Tums

 Calcium or magnesium antacids Yes  Yes 
Iron  Iron supplements Yes  Yes 
Carafate (sucralfate) Stomach protectant Yes  Yes 
Questran (cholestyramine) Bile acid sequestrants Yes  Yes 
Kayexalate (sodium polystyrene sulfonate) Potassium-removing agents Yes  Yes 
Elavil (amitriptyline)

Pamelor (nortriptyline)

 Tricyclic antidepressants Yes  Yes 
Warfarin  Blood thinner  Yes  Yes 

 

NP Thyroid and Synthroid drug warnings

Both drugs have black box warnings. A black box warning, also called a boxed warning, is the most serious warning required by the FDA. This warning states that thyroid hormones, including NP Thyroid or Synthroid, should not be used to treat obesity or for weight loss. The warning also states that taking higher doses than needed can cause serious or life-threatening toxic effects. Always take your thyroid medication exactly as instructed by your healthcare professional. Do not take more or less medication than prescribed. Thyroid replacement hormone dosages are individualized for each patient based on many factors, including lab values, age, weight, diagnosis, and other medical conditions. 

Before you take NP Thyroid or Synthroid, tell your healthcare provider about any medical conditions you have, including if you are pregnant or breastfeeding or have an adrenal gland disorder, heart problems, diabetes, or any other conditions. 

Other warnings include:

  • In older adults and people with heart disease, healthcare providers will start treatment at a lower dose to avoid the risk of heart-related side effects, including atrial fibrillation.
  • People who take NP Thyroid or Synthroid will be carefully monitored with blood tests to measure thyroid hormone levels and ensure proper dosing.
  • Neither NP Thyroid nor Synthroid should be used to treat myxedema coma (severe hypothyroidism with organ involvement), as oral medications are not used for this indication.
  • Thyroid medication may affect blood sugar levels in patients with diabetes. Close monitoring, as well as a possible dosage change in diabetes medication or insulin, may be required.
  • Over-replacement of thyroid hormone can result in lower bone mineral density. Healthcare providers will prescribe the lowest effective dose of thyroid hormone in order to minimize the risk of side effects.

Speak with your healthcare provider about whether NP Thyroid or Synthroid is better for you.

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