Brand Name vs. Generic Levothyroxine

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

Brand names for levothyroxine, the main drug used to treat hypothyroidism, include Synthroid, Levoxyl, Unithroid, and Levothroid. The generic version of levothyroxine is also prescribed, but there is some controversy about whether it is as effective and reliable as the brand names. Here's what to know about the various formulations and what the implications are if you switch from a brand name drug to the generic version.

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 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 pharmacists and patients in some cases.

The four brand name preparations of levothyroxine available in the United States for the treatment of hypothyroidism have been thoroughly tested and known to be reliable and effective, though there are some differences in how these products are manufactured.

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

Drug Consistency

Most drugs do not differ much in their generic and brand name forms, so switching between the two is not a big issue. Levothyroxine, however, is one of a handful of exceptions.


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

Given that the FDA allows such variation, it's easy to think that it can't have much effect. But levothyroxine has what's called a "narrow therapeutic window," meaning that treatment must be fine-tuned in order to achieve the desired effects.

Though the potency of one levothyroxine option may seem marginally different than another, the discrepancy could lead you to take anywhere from around a half a pill less or an entire pill more over the course of a week if you make a switch—even if you're taking the same dosage as you were before. This can dramatically influence your thyroid disease management.

Brand name levothyroxines are consistent in terms of potency from batch to batch. Generic formulations, on the other hand, tend to be less so.

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 may have symptoms of hypo- or hyperthyroidism. While this can be due to the drug's dosage and potency, it can also be due to:

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

Some people are especially prone to exacerbated symptoms when making any change to their thyroid drug regimen.


While the chemical structure and safety profiles of brand-name and generic versions themselves are the same, even a small difference in dosage strength can cause symptoms, which must be considered, especially if you are dealing with thyroid disease-related complications or co-occuring conditions, like heart disease. In addition, additional ingredients found in different versions of levothyroxine may pose safety concerns for people with allergies or sensitivities.

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 your prescribed drug's ingredients.

Additional chemicals 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. (Of course, unpleasant symptoms may be a coincidence or due to some other health problem.)

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" and "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 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 follow-up, the final TSH lab outcomes were out of range for 22.6 percent of patients in the generic levothyroxine arm vs. 20.9 percent in the Synthroid arm.

brand name vs. generic levothyroxine
Illustration by Emily Roberts, Verywell

In general, however, studies comparing generic and brand name formulations of levothyroxine fail to definitively show the advantages of one preparation over another. For example, one 2017 study found that more than 80,000 new thyroid patients taking brand-name or generic levothyroxine for a year had the same risk of cardiovascular issues requiring hospitalization (e.g. heart attack, stroke); such concerns are linked with both an underactive thyroid and the drug itself.

But there are plenty of anecdotal reports of people who have switched formulations—and felt better as a result of the change—that differences can't be dismissed entirely.

The American Association of Endocrinologists recommends taking the same brand (or generic type) of 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 brand of thyroid hormone."

Special Considerations

Despite this, there are some individuals for whom generic levothyroxine may not be advised. In particular:

  • Those 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.
  • Those with certain allergies, digestive conditions, or who have drug absorption issues: In these cases, Tirosint—a softgel option that only contains levothyroxine, gelatin, glycerin, and water—may be specifically recommended. It's important to note, however, that this drug is costly and not widely prescribed. It may not be covered by your insurance company at all or without an explanation of need from your healthcare provider.

If these situations don't apply to you and you decide that changing to a generic is the way to go for cost-saving reasons, be sure to speak with your healthcare provider about a recommended schedule for checking your TSH levels.

Thyroid Disease Doctor Discussion Guide

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

Doctor Discussion Guide Old Woman

Other tips for successfully transitioning to a generic include:

  • Getting a several-month supply: When you fill a prescription written to last you for several months, you'll ensure that you are taking medication with the same potency and ingredients for that duration.
  • Talk to your pharmacist: Once you learn that you're stable on a particular generic, ask the pharmacist if it's possible to get refills from that same manufacturer. This may not always be possible, but is worth the ask.

When Levothyroxine Isn't Enough

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

A Word From Verywell

If you are 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 from changing to a brand name product in that case.

Only you know your body. If you are not feeling good on a one preparation even though your blood tests show that you should be, it may be worth switching to a different one. The important point is to be your own advocate. Only you know how you feel. Find a healthcare provider who will work with you and listen to you, recognizing that how you are feeling, rather than test results or study findings, is what matters most.

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5 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. The US Food and Drug Administration (FDA), "Levothyroxine Sodium Product Information"

  3. London S. Generic, Brand-Name Levothyroxine Have Similar Cardiovascular Outcomes. Clinical Endocrinology News. MDedge. Published Oct. 29, 2017.

  4. Romanelli, R., Kimball, V., Dutcher, S., Pu, X., and J. Segal. 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

  5. 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

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