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July 08, 2023 7 min read

Hypothyroidism, or an underactive thyroid, is a condition where the thyroid gland does not produce enough hormones to meet the body's needs. This can lead to a range of symptoms, including fatigue, weight gain, and sensitivity to colds. One common treatment for hypothyroidism is levothyroxine, a synthetic form of the hormone thyroxine (T4), which helps to increase the levels of thyroid hormones in the body and improve symptoms.

But why do you start experiencing sensitivity to heat after taking levothyroxine? Can this medication cause the problem? Let's take a look.

What are hypothyroidism and levothyroxine?

Before diving into the topic of heat sensitivity, it's essential to have a basic understanding of how the thyroid gland works and the role of levothyroxine in treating hypothyroidism.

The thyroid gland, a butterfly-shaped organ located at the front of the neck, plays a vital role in promoting overall well-being. It produces two essential hormones, thyroxine (T4) and triiodothyronine (T3), which are crucial for regulating the body's metabolism, growth, and development. Thyroid hormones also regulate body temperature. Optimal thyroid function ensures the proper functioning of numerous bodily processes.

Hypothyroidism, a condition characterized by an underactive thyroid gland, occurs when the gland fails to produce sufficient amounts of T4 and T3. This leads to various symptoms, such as fatigue, weight gain, and muscle pain. Hypothyroid patients suffer from cold intolerance as well since low thyroid hormone can lead to difficulty regulating body temperature. Multiple factors can trigger hypothyroidism, including autoimmune dysfunction (like Hashimoto's thyroiditis), surgical removal or radiation therapy targeting the thyroid gland, or congenital conditions that affect thyroid function.

Treating thyroid dysfunction like hypothyroidism involves close monitoring since the condition leads to serious health complications, including cardiovascular issues, infertility, and, in extreme cases, thyroid cancer. Therefore, it is crucial to diagnose and treat hypothyroidism as early as possible to ensure the most favorable outcomes for affected individuals.


Levothyroxine sodium, a synthetic version of the T4 hormone, is the primary treatment for hypothyroidism. This medication helps elevate the body's thyroid hormone levels, effectively alleviating the symptoms linked to an underactive thyroid. By boosting thyroid hormone production, levothyroxine serves to restore balance within the body's various metabolic processes, allowing patients to experience relief and improved functioning.

Once a patient begins levothyroxine therapy, additional blood tests are necessary to ensure the appropriate dosing for optimal thyroid function. It is crucial that hypothyroid patients work closely with their healthcare providers to monitor symptoms and ensure that they receive the most effective and personalized treatment plan.

What is heat sensitivity?

A woman delaing with heat intolerance/heat sensitivity sitting in front of an electric fan

Heat sensitivity, or heat intolerance, is a condition characterized by an inability to tolerate heat without experiencing symptoms such as fatigue, dizziness, or nausea. In general, heat sensitivity can be caused by various factors, including dehydration, certain medications, or medical conditions like hyperthyroidism (overactive thyroid). Hyperthyroidism is a condition in which there's too much thyroid hormone in the body.

It might seem strange to link heat sensitivity with hypothyroidism, a condition typically associated with cold sensitivity. However, many hypothyroid patients, particularly those with autoimmune dysfunction, also struggle with heat intolerance.

Hashimoto's thyroiditis, a common autoimmune disorder, causes the body's immune system to attack its own thyroid tissue. This condition presents various symptoms that can differ greatly among individuals in terms of intensity and frequency. While symptoms usually start mild, they can worsen over time if the inflammation and immune response are not addressed.

People with Hashimoto's may experience symptoms of both hypothyroidism and hyperthyroidism due to the damage to the thyroid gland, which affects hormone production and overall thyroid function. When parts of the thyroid are destroyed, it can temporarily release an excess of thyroid hormones, leading to hyperthyroidism symptoms such as extreme sensitivity to heat and hot flashes. This can happen even though the patient's overall thyroid hormone levels indicate hypothyroidism.

These temporary hormone spikes can cause episodes of fatigue, hot flashes, anxiety, jitteriness, and weight fluctuations. Additionally, patients may find themselves suddenly unable to cool down when they previously had trouble staying warm, which can be quite distressing for those with hypothyroidism.

Moreover, some hypothyroid patients who take levothyroxine report having heat sensitivity as a side effect of the medication.

What is the relationship between levothyroxine and heat sensitivity?

While the exact connection between levothyroxine and heat sensitivity is not entirely understood, possible explanations for this side effect include:

1. Overmedication

One of the most common explanations for heat sensitivity in individuals taking levothyroxine is that they might be receiving too much of the thyroid hormone. Taking too much thyroid medication can push a hypothyroid patient into a hyperthyroid state, resulting in various symptoms such as heat intolerance. Therefore, it is crucial for hypothyroid patients to work closely with their healthcare providers to ensure the proper dosage and treatment for their condition.

2. Individual sensitivity to hormone fluctuations

As with any medication, individual reactions to levothyroxine can vary. It could be the case that some people are simply more sensitive to changes in their thyroid hormone levels, making them more likely to experience heat sensitivity as a side effect of the medication.

3. Levothyroxine is not for you

Levothyroxine is a synthetic form of the T4 hormone, and the body needs to convert T4 to T3, the more active thyroid hormone, for optimal functioning.

If you have impaired conversion of T4 to T3, you might not experience the full benefits of levothyroxine treatment. This could cause a relative excess of unconverted T4, leading to an imbalance in thyroid hormone levels. In some cases, this imbalance can cause heat sensitivity and other symptoms related to thyroid dysfunction.

If you suspect that levothyroxine is not suitable for them due to difficulty converting T4 to T3, you should consult with your doctor. They may consider performing additional tests, such as measuring the levels of free T3, to determine if there is an issue with T4 to T3 conversion.

Depending on the test results and your specific needs, alternative treatment options may be recommended. These alternatives can include a combination of synthetic T4 and T3 medications or natural desiccated thyroid hormone (NDT) replacements, which contain both T4 and T3 hormones. By providing more balanced thyroid hormones, these alternative treatments may help to alleviate heat sensitivity and other associated symptoms.

4. Secondary medical condition

In some cases, heat sensitivity reported by individuals taking levothyroxine might be due to an unrelated medical condition or medication. For example, some antidepressants, antihistamines, and beta-blockers are known to cause heat intolerance as a side effect.

How can you manage heat intolerance due to levothyroxine?

If you are taking levothyroxine and find yourself experiencing heat sensitivity, there are several steps you can take to help manage and alleviate your discomfort:

1. Consult your doctor

First and foremost, it is essential to discuss your symptoms and concerns with your doctor. They will be able to determine if the heat sensitivity is indeed related to your levothyroxine dosage or if there is another underlying cause. Your healthcare provider might suggest adjusting your medication dosage, changing your medication, or testing for other conditions that could be contributing to your heat sensitivity.

2. Stay hydrated

Proper hydration is crucial for overall health and well-being, but it is especially important when experiencing heat sensitivity. Ensure you are adequately hydrated by drinking water throughout the day, aiming for at least half your body weight (in pounds) in ounces daily. Avoid excessive caffeine or alcohol consumption, as these can contribute to dehydration.

3. Dress appropriately

If you know you'll be exposed to high temperatures or spending time outdoors during hot weather, dress accordingly. Opt for light, breathable fabrics and wear moisture-wicking or cooling garments if necessary. Don't forget a hat and sunglasses to protect your eyes and head from the sun.

4. Cool down your environment

Make sure your home and workspace are equipped with fans or air conditioning to maintain a comfortable temperature. If possible, avoid going outside during the hottest parts of the day and seek out air-conditioned spaces when it's too warm outdoors.

5. Develop strategies for coping with the heat

If you know you're going to be in a situation where you'll be exposed to heat, plan ahead for self-care and symptom management. For example, you could bring a small, portable fan or cooling towel to help regulate your temperature. Also, learn the signs of heat exhaustion and heatstroke and take appropriate measures if you notice any symptoms creeping up.

Can levothyroxine cause heat sensitivity?

6. Explore alternative treatment options

Heat sensitivity can be a distressing symptom for hypothyroid patients, significantly affecting their comfort and quality of life. If you've diligently tried multiple strategies to manage heat sensitivity, such as adjusting your environment, staying hydrated, and wearing appropriate clothing, but continue to struggle with this side effect, it might be time to discuss alternative treatment options with your healthcare provider.

Although levothyroxine remains the standard treatment for hypothyroidism, every patient may respond differently to the medication. In some cases, difficulties in converting T4 to the more active T3 hormone could be causing the persistence of heat sensitivity and other thyroid-related symptoms. If this is the case, it may be beneficial to switch from levothyroxine to alternative treatment options.

A combination of synthetic T4 and T3

One alternative treatment option involves using a combination of synthetic T4 and T3 medications. By providing both hormones directly, this approach may help to alleviate the challenges associated with T4 to T3 conversion and potentially lead to better symptom management, including reduced heat sensitivity.

Natural desiccated thyroid (NDT)

Another option is natural desiccated thyroid (NDT) hormone replacement, which is derived from porcine (pig) thyroid glands. NDT contains a combination of T4 and T3 hormones in a more natural form. That's why some patients find it more effective in managing their thyroid symptoms. Besides the two main thyroid hormones, it also contains T2, T1, and calcitonin, which some practitioners believe may provide a more natural and balanced hormone replacement than synthetic T4-only medications like levothyroxine.

The most popular NDT brands in the US are Armour Thyroid and NP Thyroid. However, you can also buy desiccated thyroid online in supplement form. One great option is VitaliThy, which contains porcine thyroid powder, spica prunellae siccus extract, ashwagandha extract, and selenium yeast. Plus, it's free from gluten, lactose, eggs, fish, and shellfish, as well as artificial colors and flavors.


While heat sensitivity is not a common side effect of levothyroxine, it is not entirely unheard of. It's essential to consult with your healthcare provider to manage this condition effectively, review your medication dosage, and rule out any secondary causes.

If you've tried multiple strategies to manage heat sensitivity but still struggle with this side effect, you may want to discuss the possibility of switching from levothyroxine to a natural desiccated thyroid (NDT) with your doctor. VitaliThy, a natural desiccated thyroid you can buy online, is a great option if you want to try this holistic approach to hypothyroidism treatment. This NDT supplement adheres to the high-quality standards set by the Good Manufacturing Practices of the Vietnamese Ministry of Agriculture, an institution renowned for its stringent guidelines.

Wojciech Majda
Wojciech Majda

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