Brand Name vs. Generic Levothyroxine: What is the Difference?

Is There a Difference Between Brand Name and Generic Thyroid Drugs?

Are there any important differences between generic levothyroxine and brand name drugs such as Synthroid, Levoxyl, Unithroid, and Levothroid? What should you know if you switch between different brands or generic tablets of levothyroxine? Is there one particular brand which is best?

Levothyroxine—Definition, and Use

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

Brand Name and Generic Preparations of Levothyroxine

You may be familiar with the brand name and generic preparations for different drugs. Brand name preparations are usually available first. After a period of time, other manufacturers are allowed to make the same drug. While the "drug" is the same, the inactive ingredients added to improve absorption, preserve the medications, or even add color can differ.

There are four well-tested, brand name preparations of levothyroxine available in the United States for the treatment of people with hypothyroidism (underactive thyroid): Levothroid, Levoxyl, Synthroid, and Unithroid. Although there are differences in how these products are manufactured, such as the use of coloring dyes and fillers, each of these brand-name medications is reliable.

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

Differences Between Brand and Generic Preparations

People may notice that they don't feel as well when changing from one preparation to another, and this is not surprising. While the chemical structure of these medications is the same, there can be a number ways in which they differ. For example, these drugs may differ in:

  • How much levothyroxine is in the tablet
  • How much of the levothyroxine is absorbed into the body
  • The amount of levothyroxine circulating in your body after a dose
  • Different drugs may have different potencies

While the additional chemical added to drugs are usually considered "inert" or "inactive," studies have found that these "excipients" or inactive ingredients can sometimes play a role in the effectiveness of a particular drug.

Changing Between Different Brands or Generic Preparations of Levothyroxine

If your physician has switched you from a brand name levothyroxine—such as Synthroid—to a generic version, you may experience symptoms of too much medication or not enough medication.

The American Association of Endocrinologists recommends that you should use the same brand (or generic type) of medication throughout your treatment. They continue on to say that "thyroid disease often requires lifelong therapy and is best managed with consistent and precise treatment with the same brand of thyroid hormone."

In addition, you may be given a different generic preparation of levothyroxine each time you have your prescription refilled. Practically speaking, this means your physician may need to perform more frequent blood tests and perhaps change the dose of your medication.

Although your symptoms of feeling crummy may be a coincidence or due to some other health problem, it is possible that your body was reacting to a difference between Synthroid and generic levothyroxine. It’s important that you discuss these changes with your physician.

What About Generic Levothyroxine?

In general, generic preparations of levothyroxine are usually OK, assuming you are being given the same exact generic same drug over time. Problems can arise if your pharmacy alternates between different generic preparations depending on which is the lowest cost to them. For this reason, some physicians prescribe brand name products alone to avoid this confusion.

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 suffer ill effects from changing to a brand name product at this point in time. It may, however, require you to do a little more detective work (and possibly change pharmacies) to make sure you continue to get the same generic preparation made by the same manufacturer.

The difference between brand name and generic preparations (or the switch between these that is) has been shown fairly conclusively with children who have severe congenital hypothyroidism. We'd like to argue that the switch for that child's mother who has acquired rather than congenital hypothyroidism and is caring for that child is just as important.

Of course the same can be true if you are switched from a generic brand of Levothyroxine to Synthroid. The important point is that any change in the formulation of drug you are taking can result in a change in what your body is actually receiving to work with.

Thyroid Symptoms Unrelieved by Levothyroxine Despite a Normal TSH

If your thyroid symptoms just don't seem to be responding to treatment, the first question to ask is whether you are seeing a physician who specializes in thyroid disorders. or at least has a strong interest. A physician who takes a strong interest will recognize that there are a lot of nuances in treatment, many that take careful thought. If not, you may need to switch doctors or at least get a second opinion. The "one size fits all" mentality doesn't work with thyroid disorders.

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 doing it, make an appointment with your doctor to discuss your problems.

What if Your Synthroid Does Not Work?

Bottom Line About Different Preparations of Levothyroxine

While studies have not found significant differences in effects between brand name and generic preparations of levothyroxine, it is important to continue using the preparation you have been using (or to switch to one that you plan on staying on long term) as differences can exist. From the way, the drug is absorbed in your intestine, to how much of the drug your cells actually "see," the inactive ingredients can play a role in your dose and ultimately how you feel.

It's likely that manufacturers of brand name products will boast about the benefits of their products, but studies to date fail to show advantages of one preparation over another, at least in the big picture. Only you know your body. If you are not feeling good on a generic preparation even though your blood tests show that you should be, it may be worth switching to a brand name preparation. Studies look at the response to a drug of a population of people, but people aren't populations. There are plenty of anecdotal reports of people who have switched formulations—and felt better physically as a result of the switch—to dismiss any differences entirely.

As a final note, you may have heard about natural desiccated thyroid drugs. Despite the fact that many physicians cringe when hearing of these drugs, they are effective for some people. The important point is to be your own advocate. Only you know how you feel about your thyroid preparation, whether the brand name, generic, supplemental T3 or natural desiccated product. Find a physician who will work with you and listen to you, recognizing that how you are feeling, rather than the results of the latest study, is most important.

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