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April 25, 2023 8 min read

Hypothyroidism, a condition where your thyroid gland doesn't produce enough thyroid hormones, can have a significant impact on your overall well-being. Thankfully, various treatments can help manage this condition, with levothyroxine being one of the most widely prescribed. But, like any medication, levothyroxine may cause side effects, including stomach issues. In this article, we'll discuss the possible gastrointestinal side effects of levothyroxine and offer some practical tips on how to manage them.

Let's explore the link between levothyroxine and stomach issues and how you can manage and prevent it.

What is levothyroxine?

Levothyroxine is a hormone replacement medication for people with hypothyroidism (or underactive thyroid), which is a thyroid disease that occurs when the thyroid doesn't produce enough hormone.

Thyroid hormones, mainly thyroxine (T4) and triiodothyronine (T3), are vital for keeping our metabolism, body temperature, and heart rate in check. Without enough thyroid hormone, you may experience symptoms like fatigue, weight gain, and depression. Other common symptoms include cold intolerance and joint pain. Levothyroxine helps restore normal hormone levels, alleviating these symptoms and improving our quality of life.

Levothyroxine is the synthetic form of the thyroid hormone T4. Available in various brand names and generic forms, levothyroxine is typically administered once daily, preferably in the morning and on an empty stomach. To maintain consistent thyroid hormone levels in the body, it's essential to take levothyroxine at the same time every day and avoid skipping doses. Some of the most popular brand names of levothyroxine are Synthroid, Levoxyl, and Tirosint.

How does levothyroxine work?

A woman looking healthy after taking thyroid hormone replacement therapy.

Levothyroxine works through a series of steps to ensure optimal thyroid hormone levels in the body. Upon ingestion and absorption into the bloodstream, levothyroxine is transported to the thyroid gland, as well as other tissues and cells throughout the body.

Within the cells, levothyroxine undergoes a conversion process, transforming into its active thyroid hormone form: T3. This conversion is facilitated by the action of enzymes known as deiodinases. T3 is a critical hormone responsible for regulating the body's metabolism, which is the intricate process of converting nutrients from the food we consume into usable energy.

By replacing the insufficient levels of naturally produced thyroxine (T4) with synthetic T4 in the form of levothyroxine, the body maintains a proper balance of T4 and T3 hormones. This balance is essential for sustaining normal metabolic processes, which in turn supports healthy growth, development, and overall well-being.

What are the possible stomach issues with levothyroxine?

While levothyroxine is generally well-tolerated, it can cause digestive side effects in some people. Here are the most common side effects:

1. Nausea and vomiting

Some individuals may experience nausea and vomiting shortly after starting levothyroxine. This side effect is usually mild and may go away on its own within a few days. To minimize this side effect, you can try taking the medication with food, even though it is generally recommended to take levothyroxine on an empty stomach for optimal absorption.

2. Diarrhea

Levothyroxine may cause diarrhea in some people, especially during the initial stages of treatment. This occurs because increased thyroid hormone levels can stimulate your gut to produce more digestive juices and accelerate the passage of food through your small intestines. Thus, causing diarrhea.

This side effect is typically temporary and can be managed by staying hydrated and using over-the-counter anti-diarrhea medications as needed. However, if diarrhea persists or worsens, consult your healthcare provider for further evaluation and management.

3. Abdominal pain and cramping

Some individuals may experience abdominal pain or cramping while taking levothyroxine. Drinking plenty of water, using a heating pad on the affected area, and taking over-the-counter pain relievers can help alleviate this discomfort.

4. Gas and bloating

Changes in your gut's bacterial balance can cause an uptick in gas production and bloating. While this side effect is usually mild, incorporating probiotics into your diet (either through supplements or probiotic-rich foods like yogurt) can help maintain a healthy gut environment and reduce bloating.

5. Appetite changes

Levothyroxine can sometimes alter your appetite, causing you to feel hungrier than usual. It's essential to maintain a healthy, balanced diet and avoid excessive snacking to manage your weight effectively.

6. Other digestive issues

Hypothyroidism can have a significant impact on the gastrointestinal system and cause digestive symptoms like irritable bowel syndrome (IBS), low stomach acid, constipation, gallstones, bacterial overgrowth in the small intestine, poor absorption, and abdominal discomfort. Sometimes, you may experience these symptoms even when taking levothyroxine because your dose is too low or because the medication isn't effective for you.

Could stomach issues from levothyroxine be due to allergy?

As if dealing with hypothyroidism isn't enough, some individuals may also have to worry about potential allergens in their medication. Although unusual, it's possible that stomach issues experienced while taking levothyroxine may be due to an allergy to one or more of the ingredients present in the medication. If you have an allergic reaction to levothyroxine, your stomach issues will also be accompanied by symptoms like chest pain, skin rash, flushing, fever, and wheezing.

Here are some of the potential allergens in levothyroxine:


Did you know that one of the common fillers used in many levothyroxine brands is confectioner's sugar (powdered sugar), which contains cornstarch? Interestingly, some studies discovered that corn proteins could cross-react with gluten, potentially triggering an immune system reaction similar to that of gluten exposure. This could be particularly concerning for those with corn allergies.

But although this cross-reactivity might affect individuals with celiac disease or non-celiac gluten sensitivity, gluten itself isn't necessarily an issue.

A 2017 study specifically investigated the gluten content in Synthroid tablets. And the researchers found the level of gluten in Synthroid to be below detectable limits (meaning, according to FDA criteria, Synthroid would be considered gluten-free). Even though the exact amount of gluten that could worsen celiac disease symptoms is unknown, it's unlikely that Synthroid would exacerbate symptoms for those living with celiac disease. But still, if you have gluten sensitivity or celiac disease and experience stomach issues after taking levothyroxine, it might be a good idea to talk to your doctor.


Aside from cornstarch, many levothyroxine tablets also contain lactose. This might cause some trouble for those with lactose intolerance, which is a condition where the body struggles to digest lactose, the main sugar found in milk.

If you're lactose intolerant, you might experience symptoms such as abdominal pain, digestive tract discomfort, cramps, bloating, gas, nausea, and diarrhea. These signs typically start anywhere between 30 minutes to two hours after taking levothyroxine.


Did you know that acacia, a family of shrubs and trees, is used as an ingredient (acacia gum) in some medications, including some brands of levothyroxine? Acacia helps provide form and shape to tablets. Surprisingly, some people with pollen allergies and hay fever, especially those allergic to tree and grass pollens like ryegrass pollen, might also have an allergy to acacia—even when it's an ingredient in the medication.

It's worth noting that people with asthma are more likely to be allergic as well. Hypothyroidism patients with these allergies may experience allergic symptoms when taking levothyroxine. And here's an interesting tidbit: those with seasonal allergies might discover that they don't respond well to their levothyroxine during allergy season.

While studies examining the incidence of acacia sensitivity are limited, it seems that people living in Iran, surrounding countries, and the Philippines have a particularly high rate of sensitization. So, if you're concerned about potential allergies to acacia, make sure to discuss it with your healthcare provider to find the best solution tailored to your needs.

Color additives

Some levothyroxine formulations contain color additives, particularly in the outer coating of the tablet. In rare cases, these color additives may trigger allergic reactions or stomach issues.

Other binders and fillers

In addition to the ingredients mentioned above, levothyroxine tablets contain various other inactive ingredients, or excipients, that function as binders and fillers to give the tablet its structure. Some individuals may have a sensitivity or allergy to these excipients, which may contribute to stomach issues.

How to manage and treat stomach issues due to levothyroxine?

Healthy food may help manage stomach issues due to levothyroxine

If you're experiencing stomach issues while taking levothyroxine, these practical tips can help:

  1. Take levothyroxine on an empty stomach: Levothyroxine should be taken on an empty stomach at least 30 minutes to 1 hour before eating breakfast. This is because food can interfere with the absorption of levothyroxine and reduce its effectiveness.

  2. Consistency is key: Taking levothyroxine at the same time every day helps to maintain consistent levels of thyroid hormone in the body. This can help to reduce the risk of stomach problems and other side effects related to fluctuating thyroid hormones.

  3. Boost your gut health: Incorporating probiotics into your diet, either through supplements or probiotic-rich foods like yogurt and kefir, can help promote a healthy gut environment. A balanced gut can contribute to reducing stomach issues like bloating and discomfort.

  4. Make sure your body is well hydrated: Staying well-hydrated can alleviate abdominal pain and diarrhea. Drinking plenty of water throughout the day also supports overall health and well-being.

  5. Embrace a healthy lifestyle: Maintaining a healthy, balanced diet and engaging in regular physical activity can work wonders for your digestive system. A balanced, nutrient-rich diet and exercise can help prevent or lessen stomach issues related to levothyroxine.

  6. Keep your healthcare provider in the loop: If your side effects persist or worsen, don't hesitate to consult your healthcare provider. They can assess your situation and recommend appropriate interventions or adjustments to your medication regimen.

  7. Consider switching to a different brand of levothyroxine: Some people may experience stomach issues with certain brands of levothyroxine. If you are experiencing stomach problems, talk to your doctor about switching to a different brand of levothyroxine. For example, if you've been taking Synthroid, you might want to try Tirosint.

What to do if you keep experiencing stomach issues while on levothyroxine?

If you're still struggling with stomach issues even after following the tips mentioned earlier, it might be time to discuss an alternative thyroid medication for hypothyroidism with your doctor. There are other medications available that may be better tolerated by your body. One of the most popular alternatives is natural desiccated thyroid (NDT).

NDT is derived from dried pig thyroid glands and contains both T4 and T3 thyroid hormones. Some individuals may not tolerate levothyroxine well if their body struggles to convert T4 to T3. However, they might find NDT more effective since it already contains both hormones.

Additionally, several NDT brands are free of lactose and gluten, making them suitable for those with lactose intolerance or gluten sensitivity. The brands Nature Throid and WP Thyroid are all-natural and free of both lactose and gluten, but they aren't available anymore. One good alternative is VitaliThy, a natural desiccated thyroid you can buy online.

VitaliThy is an NDT supplement manufactured in Vietnam. It uses Thyroid (USP) as its active ingredient, meaning it includes both T4 and T3. Furthermore, it's free from common allergens like lactose, gluten, artificial coloring, artificial flavoring, eggs, fish, and shellfish. As a result, individuals with food sensitivities can enjoy its benefits without worrying about adverse side effects.

Conclusion: Stomach issues are a common side effect of levothyroxine

Levothyroxine is an essential medication for managing hypothyroidism, but it can cause stomach issues in some people. By following the tips mentioned above and staying in close communication with your healthcare provider, you can help mitigate these side effects and continue reaping the benefits of this crucial treatment.

If the digestive problems persist, consider switching your levothyroxine to natural desiccated thyroid (NDT). One great option is VitaliThy, a natural desiccated thyroid you can buy online. This NDT supplement is gluten- and lactose-free. Plus, it doesn't contain any fish, shellfish, or eggs in its ingredients. It's also free of artificial coloring and flavoring.

Wojciech Majda
Wojciech Majda

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