Levothyroxine and Sinus Problems: What You Should Know

For decades, researchers have shown a link between low thyroid and sinus problems like nasal stuffiness, sinus congestion, and impaired hearing. This is because lack of thyroid hormone allows a chemical to accumulate in the face and cause puffiness.

Some people with thyroid issues may not experience sinus problems until they begin to take levothyroxine (Synthroid) to treat their hypothyroidism. However, the treatment is not the cause of the sinus problems—in fact, it's typically a sign the dosage is not right.

It's tough to get the exact dose of levothyroxine right for people with hypothyroidism, because each person is different. Here's what to know about what happens when thyroxine levels are too high and too low, and how they affect the sinuses in particular.

Levothyroxine and Side Effects

Levothyroxine (Synthroid) is an oral medication typically used to treat hypothyroidism, a condition in which the thyroid gland doesn't produce enough thyroid hormone. In some cases, the thyroid doesn't make enough of a hormone called thyroxine, or T4. This is where levothyroxine comes in.

Levothyroxine is a synthetic version of thyroxine. At the right doses, it can restore normal thyroxine levels in the body.

The side effects you're likely to experience while taking levothyroxine can vary significantly depending on your dosage. Typically, adverse reactions are a result of the dose being too high or too low, rather than anything in the medication itself.

As the thyroid's role in the body is highly systemic—affecting multiple organs and tissues at the same time—the side effects typically experienced with levothyroxine are also systemic.

Possible side effects of too high of a dose (which is extremely rare) include:

Cardiovascular problems, such as angina pectoris (lack of blood and oxygen to a part of the heart), irregular heartbeat, heart failure, and fast heartbeat
Difficulty breathing
Muscle spasms and tremors
Headache
Anxiety, hyperactivity, and irritability
Insomnia
Muscle weakness
Weight loss
Gastrointestinal issues, such as diarrhea, increased appetite, and vomiting
Heat intolerance
Fatigue

The cardiovascular problems caused by levothyroxine can be especially dangerous, even fatal. They are also more likely to occur if you have a history of heart disease.

Hypothyroidism can, in rare cases, cause a heart condition called sinus node dysfunction, also known as sick sinus syndrome. It doesn't have anything to do with your nasal passages, though: This is when electrical signals important to a part of the heart called the sinoatrial node—your natural pacemaker—don't function properly. This can affect your heartbeat in potentially dangerous ways.

Talk with your health care provider before you start taking levothyroxine to reduce your risk of any unexpected adverse effects, especially if you have a history of heart problems.

Some research indicates the side effects of levothyroxine can still be a problem even if the medication returns your thyroxine to normal levels.

A study carried out at the University of Groningen in the Netherlands in 2018 looked at the medical information of 34,440 people that had been recorded as part of a prior Dutch Lifelines study. The University of Groningen study looked at participants' medical histories, medications, thyroid hormone levels, and quality of life. The study found that around 10% of people who had been using some kind of thyroid hormone treatment and whose thyroid hormone levels were back within a normal range still experienced adverse effects.

Low Thyroid and Sinus Health

Hypothyroidism is known to increase your risk of developing sinus problems, especially acute sinusitis (inflammation of the nasal passages). This could be a result of the increase in blood pressure long associated with low thyroid or the accumulation of glycosaminoglycans—which help cells throughout the body with growth and repair—in the face.

Another possible sinus problem to be aware of is rhinitis. Allergic rhinitis, in which the mucous membranes in your nose become itchy and inflamed, can cause a wide range of symptoms, including nasal congestion and sneezing. As the name suggests, allergic rhinitis is usually caused by exposure to allergens.

There may be some connection between hypothyroidism and another condition called non-allergic rhinitis, which has very similar symptoms but is not caused by the presence of allergens.

One 2021 study published in the World Journal of Otorhinolaryngology: Head and Neck Surgery (WJOHNS) looked at the possible connections between non-allergic rhinitis and hypothyroidism, as well as a few other conditions. One hundred and three people participated in the study and 22 (21.4%) had both non-allergic rhinitis and hypothyroidism. The participants in this group mostly reported experiencing headaches and nasal congestion.

The researchers suggested that non-allergic rhinitis might be directly caused by hypothyroidism in these cases. This is thought to be because nasal mucous membranes contain receptors for thyroid hormones, which are a vital part of how your body processes those hormones.

A lack of thyroid hormones because of hypothyroidism leads to inflammation and trapped fluid in the mucous glands, causing them to swell. The study also suggests that this causes the body to produce more of a connective tissue called cartilage inside the nasal cavity, closing it up further.

These issues may be perceived as side effects of levothyroxine, but actually may be a sign that your dose is too low. Talk with your doctor if you experience swollen sinuses while taking the medication.

Decongestants and Thyroid Health

Sinusitis is a very common condition. In the US, 28.9 million people are diagnosed with sinusitis every year, according to the Centers for Disease Control and Prevention (CDC). The actual number is likely much higher than this, as it only accounts for people who have been officially diagnosed with chronic sinusitis; many choose to treat its symptoms at home.

As nasal congestion is one of the most prevalent symptoms, it's usually recommended that you use decongestants to relieve the symptoms. The active ingredients in many decongestants are pseudoephedrine and phenylephrine (both found in Sudafed and its store-brand versions). These medications reduce the flow of blood to your sinuses and slow down the rate at which your glands produce mucus.

Decongestants can have certain side effects that you should be aware of. Pseudoephedrine can make your heart rate irregular, meaning that it doesn't beat at the same rate consistently. It can also raise your blood pressure.

It's also crucial to be aware of which decongestants to take and to not take if you are on levothyroxine, because of potentially dangerous interactions.

Decongestant Interactions with Thyroid Medication

Always talk to your health care provider before you take any medication, including over-the-counter drugs. Many medications interact with each other in unhealthy ways.

For example, many decongestants are known to interact with levothyroxine, which can make the effects that both medications have on your heart more serious.

This risk means that levothyroxine and decongestants with pseudoephedrine or phenylephrine aren't recommended together in most circumstances. You should only take them together if this is specifically recommended by your health care provider. This is particularly important for people who already have some form of cardiovascular health problem, like coronary artery disease.

Dr. Peter Manes, an associate professor of surgery at Yale Medical School, stated: "Using [levothyroxine] with some sinus medications, such as phenylephrine, can possibly lead to heart issues, including high blood pressure, palpitations, chest pain, and irregular heartbeat. I would advise these patients to use oral antihistamines, topical nasal steroids, and nasal saline irrigations."

Low Thyroid Affects Sinuses; Take Care with Treatment

Though some elements of the relationship between hypothyroidism and nasal health problems need more study, there is plenty of evidence of a direct connection between the two. The use of medications like levothyroxine at too high or too low doses are known to cause a range of adverse effects on various parts of your body, with cardiovascular health being especially important to consider.

Over-the-counter decongestants also cause issues with blood pressure and heart rate, which may then be worsened by interactions with levothyroxine. More study is needed to confirm whether levothyroxine is a cause for sinus health problems.

Thyroid Issues and Sinus Problems

Can thyroid problems affect sinuses?

A connection between thyroid and sinus problems is well established. If you don't have enough thyroid hormone, the mucous membranes in your sinuses can swell, causing congestion.

Can hypothyroidism cause sinus node dysfunction?

There is some evidence to suggest that sinus node dysfunction—a heartbeat rhythm disorder—is caused by hypothyroidism, but this is thought to be rare.

Can levothyroxine cause head pressure?

This is unlikely. Hypothyroidism itself is thought to contribute to increases in pressure in the skull in some cases, but there isn't much evidence to suggest that this is due to the use of levothyroxine.

Why does hypothyroidism cause rhinitis?

The mucous membranes in your sinuses are home to thyroid hormone receptors. If the level of thyroid hormones in your system is too low, these receptors may cause non-allergic rhinitis, in which your mucous glands swell and your body overproduces connective tissue, blocking up your nasal passages.

Synthroid (levothyroxine sodium tablets, USP): https://www.accessdata.fda.gov/drugsatfda_docs/label/2008/021402s011lbl.pdf

Tudoran M, Tudoran C. Hyperthyroidism and Sick Sinus Syndrome, a Rare but Challenging Association: a Study of Three Cases. Nigerian Journal of Clinical Practice. 2017;20(8). doi:10.4103/njcp.njcp_288_16

Hawks MD M, Paul MD M, Malu MD O. Sinus Node Dysfunction. aafporg. 2021;104(2):179-185.

Some Patients on Levothyroxine Continue to Experience Symptoms despite Normal Thyroid Hormone Levels: https://www.endocrine.org/news-and-advocacy/news-room/2018/patients-on-levothyroxine-continue-to-experience-symptoms-despite-normal-thyroid-hormone-levels

Acute & Chronic Sinusitis Treatment NYC: https://www.mountsinai.org/care/ent/services/nasal-sinus-allergy/conditions/sinusitis

Fawzan AE, Assiri SA, Althaqafi RMM, et al. Association of Allergic Rhinitis with hypothyroidism, asthma, and Chronic sinusitis: Clinical and Radiological Features. World Journal of Otorhinolaryngology - Head and Neck Surgery. Published online March 12, 2021. doi:10.1016/j.wjorl.2020.12.001

Chronic Sinusitis: https://www.cdc.gov/nchs/fastats/sinuses.htm

Don't Let Decongestants Squeeze Your Heart: https://www.health.harvard.edu/heart-health/dont-let-decongestants-squeeze-your-heart

Pseudoephedrine (including Sudafed): https://www.nhs.uk/medicines/pseudoephedrine/

Levothyroxine and Sudafed Congestion Interactions: https://www.drugs.com/drug-interactions/levothyroxine-with-sudafed-congestion-1463-0-1964-16108.html

Eghtedari B, Correa R. Levothyroxine. StatPearls. September 4, 2022. Accessed November 4, 2022. https://www.ncbi.nlm.nih.gov/books/NBK539808/

Notes: This article was originally published December 2, 2022 and most recently updated December 8, 2022.

Martyn Bryson is a medical writer living in Philadelphia. They have over a decade of experience as a writer and editor covering a wide range of health and wellness topics.

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