Brand Name vs. Generic Levothyroxine

There are important factors to consider before taking one or the other

Like many people, you may be in the habit of asking for the generic equivalent of a medication to save money. But if you take levothyroxine, the main drug used to treat hypothyroidism, whether to use a generic versus a name-brand drug may need to be considered carefully.

Levothyroxine is sold under several brand names, including Synthroid, Levoxyl, Unithroid, and Levothroid. A generic version of levothyroxine is also available. But there is some controversy about whether it's as effective and reliable as the brand-name versions.

This article explains how the potency can vary between brand-name and generic versions of levothyroxine. It also explains the possible consequences of switching, as well as when a brand-name product is the best choice.

Levothyroxine Preparations

Levothyroxine is a synthetic (man-made) version of thyroxine, or T4, the main hormone that is made and released by your thyroid gland. Levothyroxine is prescribed for people with an underactive thyroid, a condition known as hypothyroidism.

Most medications are available in brand-name and generic preparations. Brand-name preparations are usually the first ones available on the market. After a period of time, other manufacturers are allowed to make generic versions of the same drug.

While the active ingredient is the same, the inactive ingredients added to improve absorption, preserve the drug, or add color can differ. Generic preparations may be less expensive for patients and pharmacists.

The brand-name preparations of levothyroxine available in the United States for the treatment of hypothyroidism have been thoroughly tested. They are known to be reliable and effective.

The Food and Drug Administration (FDA) has also approved the use of generic levothyroxine, which is made by several different pharmaceutical companies.

Drug Consistency

Most brand-name drugs do not differ much from their generic counterparts, so switching between the two is not an issue. Levothyroxine, however, is one of a handful of exceptions. The versions differ in two key ways: potency and added ingredients (which are usually inactive).


Manufacturers of any preparation of levothyroxine must ensure that their drug is within 5% of its stated potency, which must be between 95% and 105%, per the FDA. This leaves room for small, but meaningful, differences between levothyroxine products.

Given that the FDA allows such a variation, it's easy to think that it won't make much difference which type you take. But levothyroxine has a "narrow therapeutic window," meaning that treatment must be fine-tuned to achieve the desired effects.

The potency of one levothyroxine option may seem only slightly different from another. But that difference could add up to the equivalent of anywhere from about half a pill less to an entire pill more than your intended dosage over the course of a week—even if you take your usual dosage as prescribed.

That can dramatically influence your thyroid disease management.

If you switch from a brand-name to a generic preparation, you may notice that you don't feel as well on the generic drug. And you may develop symptoms of hypothyroidism or hyperthyroidism, such as fatigue, numbness or tingling in your hands, whole-body soreness, or dry skin.

While the drug's potency may trigger these symptoms, they could also be triggered by:

  • How much of the levothyroxine is available for absorption by your body
  • The amount of levothyroxine circulating in your body after a dose

From batch to batch, brand-name levothyroxine products are consistent in terms of potency. Generic formulations tend to be less so.

Other Ingredients

Fillers and additives such as dyes, gluten, and lactose are also less consistent in generics than brand-name options because they originate from different manufacturers. If this is a concern for you, ask your pharmacist for a list of the ingredients in your prescribed drug.

Ingredients added to drugs are usually considered "inert" or "inactive." But studies have found that these inactive ingredients can sometimes decrease the effectiveness of a particular drug.

They could also pose problems for people with allergies or sensitivities.

Dispense As Written

If you are certain that you need to stick with a particular brand of levothyroxine, make sure your healthcare provider writes "DAW" (dispense as written) or "no generic substitution" on your prescription.

Brand vs. Generic: What the Research Says

According to a presentation at the annual meeting of the American Association of Clinical Endocrinologists in 2017, Synthroid was associated with significantly better thyroid-stimulating hormone (TSH) lab results than generic levothyroxine.

The study's authors looked at hypothyroidism patients between January 2008 and March 2016 who were started on either Synthroid or generic levothyroxine within a year of being diagnosed.

During their follow-up, the final TSH lab outcomes were "out of range" for 22.6% of patients who took the generic levothyroxine and 20.9% for those who took Synthroid. In other words, Synthroid produced better results.

brand name vs. generic levothyroxine

Verywell / Emily Roberts

In general, however, studies comparing generic and brand name formulations of levothyroxine fail to definitively show advantages of one preparation over another.

For example, one 2017 study of more than 80,000 new thyroid patients found that those taking either brand-name or generic levothyroxine for a year had the same risk of cardiovascular issues requiring hospitalization (such as heart attack and stroke).

There are plenty of anecdotal reports of people who have switched to a brand-name formulation and felt better as a result. You may wish to ask your healthcare provider what they make of these reports.

The American Thyroid Association recommends taking the same brand-name (or generic) medication throughout your treatment. The association emphasizes that "thyroid disease often requires lifelong therapy and is best managed with consistent and precise treatment with the same (type) of thyroid hormone."

Special Considerations

For health reasons, generic levothyroxine may not be the better choice for people who:

  • Have had thyroid cancer. Fluctuating TSH, which can occur from inconsistent thyroid hormone replacement, can affect the body's ability to prevent cancer from returning. Discuss treatment options with your healthcare provider.
  • Have certain allergies, digestive conditions, or who have drug absorption issues. In these cases, Tirosint—a soft gel option that contains levothyroxine, gelatin, glycerin, and water—may be recommended. Note, however, that this drug is costly and not widely prescribed, and your insurance company may not cover it.

Thyroid Disease Doctor Discussion Guide

Get our printable guide for your next doctor's appointment to help you ask the right questions.

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When Levothyroxine Isn't Enough

Whether they take a brand name or a generic form of levothyroxine, some people continue to experience symptoms of hypothyroidism even when their TSH is normal.

The addition of T3 to T4 "monotherapy" may result in better control of symptoms and quality of life. If your thyroid preparation doesn't seem to be helping, make an appointment with your healthcare provider to discuss a solution.


Most brand-name drugs do not differ that much from their generic counterparts, so switching between the two is not an issue. Levothyroxine, however, is an exception.

When some people try to switch from a brand name to a generic (often to save money), they experience fatigue, numbness or tingling in their hands, whole-body soreness, or dry skin. Other people simply aren't suited to the generic formulation, primarily because of pre-existing health issues. To make the best decision, consult your healthcare provider.

A Word From Verywell

If you're feeling good and your blood tests are stable on a generic form of levothyroxine, by all means, continue to use that preparation. You are more likely to experience ill effects by changing to a brand-name product.

Remember that no one knows your body like you do. And you have to be your own best advocate, working alongside a healthcare provider who will listen to you and guide you to the right solution.

10 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. American Thyroid Association. Thyroid hormone treatment.

  2. U.S. Food and Drug Administration. Generic drugs: questions & answers.

  3. U.S. Food and Drug Administration (FDA). Levothyroxine sodium product information.

  4. Food and Drug Administration. Real-World Evidence from a Narrow Therapeutic Index Product (Levothyroxine) Reflects the Therapeutic Equivalence of Generic Drug Products.

  5. National Institutes of Health. Hypothyroidism.

  6. Pottel J, Armstrong D, Zou L, et al. The activities of drug inactive ingredients on biological targetsScience. 2020;369(6502):403-413. doi:10.1126/science.aaz9906

  7. Han DH. Brand vs. generic levothyroxine: Effect on TSH lab data compared. MPR.

  8. Romanelli R, Kimball V, Dutcher S, Pu X, Segal J. Provider and patient determinants of generic levothyroxine prescribing: an electronic health records-based study. The Annals of Pharmacotherapy. 2017 Apr 1. (Epub ahead of print). doi:10.1177/1060028017705393

  9. American Thyroid Association. What are the differences in thyroid preparations?

  10. Carswell JM, Gordon JH, Popovsky E, Hale A, Brown RS. Generic and brand-name L-thyroxine are not bioequivalent for children with severe congenital hypothyroidism. J Clin Endocrinol Metab. 2013;98(2):610–617. doi:10.1210/jc.2012-3125

Additional Reading

By Michael Bihari, MD
Michael Bihari, MD, is a board-certified pediatrician, health educator, and medical writer, and president emeritus of the Community Health Center of Cape Cod.