Brand vs. Generic Levothyroxine: Key Differences and What Happens If You Switch

What Is Levothyroxine?

Levothyroxine is a medication that’s used to treat low thyroid levels, also called hypothyroidism. Hypothyroidism is a condition where your thyroid gland doesn’t make enough thyroid hormone.

Your thyroid hormones play a major role in regulating your metabolism, or how your body makes and uses energy. There are two main types of thyroid hormone — thyroxine (T4) and triiodothyronine (T3).

Levothyroxine is a laboratory-made version of T4. It works by replacing the T4 hormone that’s normally made by the thyroid. Some people with hypothyroidism may take a laboratory-made version of T3 called liothyronine. However, levothyroxine is the most common type of thyroid hormone replacement.

Levothyroxine is a medication with a narrow therapeutic index. This means that even small differences in the dose can make a big difference in how your body responds to it. Because of this, some health experts recommend sticking to the same brand of levothyroxine to minimize changes that could affect how well it works.

What’s the Difference Between Generic and Brand-Name Drugs?

Both generic and brand-name medications have the same active ingredient. The generic name of a medication is the same as the active ingredient.

The brand name of a medication is the name assigned to the drug by the manufacturer. When a pharmaceutical company develops a new drug, they will name the active ingredient (generic name) and give it a brand name. A brand name may also be called the proprietary name of the drug.

Different countries may set absorption parameters for bioequivalence of generics. For example, in the United States, a generic version of a brand product that shows 20% less absorption or up to 25% more absorption is generally considered therapeutically equivalent, though this range may be too broad for narrow therapeutic index drugs like Levothyroxine.

Inactive Ingredients

The main difference between brand and generic drugs is the inactive ingredients. Inactive ingredients are components of the medication that don’t have a direct effect on your body. Some inactive ingredients help the active ingredient work better, make the drug more stable, or help the drug dissolve. Before a generic drug is approved, the manufacturer must prove that the differences in inactive ingredients don’t affect how the drug works in your body.

In the United States (U.S.), the Food and Drug Administration (FDA) reviews drug safety and efficacy data to make sure a generic medication has the same strength, purity, and quality as the brand. In Canada, Health Canada regulates the approval of medications. There are strict quality and efficacy requirements that a drug manufacturer must meet before a new or generic drug is approved.

Cost

Another difference between brand-name and generic medications is the cost. In general, generic drugs are usually less expensive than their brand-name counterparts. Drug manufacturers can often set the price of a generic medicine lower than the brand because it doesn’t cost as much to develop a generic drug. Additionally, if there are several different generic drugs available on the market, competition can also drive the price lower.

Appearance

The appearance of different brand and generic formulations of levothyroxine will also be different. The pills of different brands of levothyroxine may have a different shape, color, and imprint.

If your levothyroxine pills look different than you expect, check with your pharmacist to make sure they are the correct pill.

What Are the Brand-Name Medications Available for Levothyroxine?

Several different manufacturers make levothyroxine. Many drug makers give levothyroxine a brand name in addition to the generic name. Examples of brand names of levothyroxine available in the U.S. include:

In Canada and Europe, other brand names of levothyroxine may be available, including Eltroxin and Euthyrox.

There are also several different generics of levothyroxine available, each made by a different manufacturer. Generic levothyroxine formulations will go by the name levothyroxine or levothyroxine sodium. Genpharm and Mylan are drug manufacturers that make the most commonly available generic levothyroxine in the U.S.

Is Brand Levothyroxine Better Than Generic?

Several clinical studies have found that brand and generic levothyroxine work equally as well.

In a 2020 study co-written by the FDA, researchers found that generic levothyroxine was as effective as the brand-name drug for treating mild thyroid disease. This study included more than 17,000 adults in the U.S. who recently began taking either brand or generic levothyroxine. Researchers found that the percentage of people who achieved normal thyroid hormone levels within 3 months was the same for people on generic or brand levothyroxine.

Another study from 2021 found that people taking Synthroid were slightly more likely to have thyroid hormone levels in the desired range than people taking generic levothyroxine. This study included more than 18,000 adults in the U.S. In the study, 78.5% of people taking Synthroid and 77.2% of people taking generic levothyroxine achieved their target thyroid hormone levels within 12 months. Although the difference is less than 1%, the researcher found that it was a statistically significant result. This means the results are unlikely to be due to chance.

The cost of the medication is another important factor when considering which is better for you. As mentioned before, brand-name medications are often more expensive than generic medications. Some insurance companies may only cover a brand-name medication after you’ve already tried a lower-cost generic. A medication can only be effective if you can afford it and take it regularly. A lower-cost generic levothyroxine may help you stay on track with taking your medication. If you’re having trouble affording your medication, talk to your physician or pharmacist about lower-cost options that may be available for you.

Can You Switch From One Generic Levothyroxine to Another?

Research has found that switching from one generic levothyroxine formulation to another doesn’t result in significant differences in thyroid hormone levels.

Researchers in a 2022 study aimed to find out whether switching from one generic levothyroxine to another would impact thyroid hormone levels. In this study, some participants stayed on the same generic levothyroxine while other participants switched from one generic to another. After 3 months, about the same percentage of people in each group had normal thyroid hormone levels. These results suggest that switching from one generic levothyroxine to another doesn’t have a negative effect on thyroid hormone levels.

Are There Any Situations Where The Brand Is Preferred Over the Generic?

Your physician may recommend you switch to a brand name medication if you’re not responding as expected to your medication. Some physicians may recommend sticking to a brand of levothyroxine in young children, pregnant people, or people with certain medical conditions, such as:

Some physicians may recommend taking the brand levothyroxine for other reasons. If you have any concerns about whether the brand or generic levothyroxine is better for you, talk to your physician.

What Should You Do After Switching From One Levothyroxine Brand to Another?

Even if you try to stick to the same levothyroxine brand or generic formulation, sometimes switching is unavoidable. For example, your insurance may require you to take another brand, or your usual brand may be unavailable. If you have to switch from one brand to another, research suggests that most people don’t see any significant changes in their thyroid hormone levels. However, it’s possible not everyone will react the same way.

In the weeks after switching from one brand or generic of levothyroxine to another, there are a few things you should keep in mind.

Take Your Medication the Same Way

If you switch from one brand or generic to another, keep taking your medication exactly the same way as you always have. Taking your medication the same way will help your physician more accurately track any changes in your thyroid hormone levels.

It’s best to take levothyroxine on an empty stomach, at least 30 minutes before eating. Food and other medications may affect how well levothyroxine is absorbed into your bloodstream. Many people take levothyroxine first thing in the morning before eating or taking other medications.

Your physician or pharmacist can help you figure out the best time to take levothyroxine based on your daily schedule and other medications.

Re-Check Your Thyroid Hormone Levels

To make sure your thyroid hormone levels are still within the desired range after starting a new generic or brand, your physician will recheck your thyroid hormone levels.

You won’t see any changes right away because it takes several weeks for your thyroid hormone levels to stabilize after you start taking the new medication. Your physician may ask you to come back for blood work within 6 to 8 weeks after starting. Once your thyroid hormone levels are stable and within the desired range, you may be able to check thyroid hormone levels less often.

Monitor How You Feel

You should also monitor how you feel and be aware of the symptoms you may experience if your thyroid hormone levels are too high or too low.

If your thyroid hormone levels are too high, you may have symptoms, such as:

If your thyroid hormone levels are too low, you may have symptoms, such as:

Symptoms related to changes in your thyroid hormones usually develop slowly over time. You likely won’t notice any changes right away. Additionally, you may not have any symptoms of high or low thyroid hormones. That’s why it’s so important to re-check your thyroid hormone levels with a blood test to find changes you’re not able to feel.

If you notice any changes in how you feel while taking a new formulation of levothyroxine, talk to your physician right away.

Talk To Your Health Care Team

With so many different brand and generic options for levothyroxine, it can feel overwhelming to choose the right one for you. To make it more difficult, recent research suggests that brand and generic formulations are equally effective, and switching between different generics doesn’t affect thyroid hormones. This means that choosing the right brand may not be as important as previously thought.

Even with this research, some physicians are still more likely to prescribe brand-name levothyroxine than a generic formulation. This is especially true for endocrinologists — doctors who specialize in treating hormone-related health conditions. However, the FDA and other regulatory agencies have strict standards for generic levothyroxine products.

Before you start taking brand or generic levothyroxine, talk to your physician about what’s important to you, including medication cost. You should also ask your physician about their experience with a specific brand or generic levothyroxine.

Sometimes, physicians may notice that some people do better on one formulation of levothyroxine compared to another.

The best formulation of levothyroxine for you is the one you can afford and will take regularly. Your health care team and pharmacist can help you navigate the available choices.