How Thyroid Medication Side Effects Can Affect Your Life

How Thyroid Medication Side Effects Can Affect Your Life

Why Understanding Your Numbers Is Critical to Getting the Proper Treatment

Thyroid medication side effects: woman that fell asleep on a couch

At least once a week, we have patients coming into our clinic who are experiencing thyroid medication side effects like: 

  • Fatigue 
  • Chest pain
  • Hair loss 
  • Irregular heartbeat/palpitations
  • Insomnia
  • Skin rash/flushing
  • Excessive sweating
  • Nervousness
  • Irritability
  • Other symptoms of hyperthyroidism [1]

And in each case, we find that these patients are either being overmedicated for low thyroid hormone or being medicated when they shouldn’t be at all.

Let’s be clear: Some people do need thyroid medication, and they should take it at the appropriate dosing. But unfortunately, medication for hypothyroidism is being overprescribed, causing potentially serious side effects for those with subclinically low levels of thyroid hormone. 

This isn’t because these meds are unsafe — in fact, prescription medications like levothyroxine sodium (Synthroid/Unithroid/Tirosint are brand names) or natural thyroid gland (Thyrolar or Liotrix) seem to have only rare serious side effects when used appropriately.

But there are many misconceptions about healthy thyroid hormone levels, and sometimes medical practitioners make the decision to prescribe thyroid medication based on a theory about those levels that a significant amount of research has now disproven. 

Those decisions can actually be dangerous to patients with subclinical hypothyroidism or “sluggish” thyroid. Hypothyroidism is incredibly treatable using conventional prescription medication, but this doesn’t tell the whole story. There’s a difference between hypothyroidism and subclinically low levels of thyroid hormone. In fact, a 2021 meta-analysis showed that around 30% of patients taking thyroid meds didn’t need to be taking them at all [2 Trusted SourcePubMedGo to source]. An earlier study showed up to 60% of patients were taking unnecessary thyroid medication (their thyroid hormone levels remained normal after discontinuation, and they did not experience symptoms of hypothyroidism) [3 Trusted SourcePubMedGo to source].

To get a clearer picture of hypothyroidism and thyroid medication side effects, let’s go over what your thyroid does, the symptoms of hypothyroidism, and why overtreatment can create unwanted issues. Then I’ll help you determine whether or not you should be taking thyroid medication. 

Thyroid Function 101

Thyroid medication side effects: doctor examining a patient's throat

Your thyroid gland is a small, butterfly-shaped gland that wraps around your trachea at the front of your neck. It’s part of the endocrine system and produces important hormones that help regulate your energy, digestion, body weight, temperature, sex hormones, cardiovascular function, and nervous system. 

When things go awry in your system — autoimmunity, chronic stress, an adverse drug reaction, thyroid cancer, etc. — your thyroid gland can become inflamed (thyroiditis), resulting in either over- or underproduction of thyroid hormone. 

When your body overproduces thyroid hormone (overactive thyroid), you have hyperthyroidism (also called Graves’ disease, although this isn’t the only form of hyperthyroidism). Hyperthyroidism can lead to an enlarged thyroid or nodules that are visible in your neck (goiter), in addition to eye protrusion (a bug-eyed look). 

When your body doesn’t make enough thyroid hormone, you have hypothyroidism, often associated with the autoimmune disease Hashimoto’s thyroiditis, although this isn’t the only cause of hypothyroidism [4]. Hashimoto’s thyroiditis is 10 times more common in women than men [5 Trusted SourcePubMedGo to source].

Each of these thyroid problems can vary in seriousness, depending on just how low or high your thyroid hormone levels are, which is where the potential issues of overmedication can come into play. However, if a serious case of thyroiditis goes untreated for a long time, major health problems can arise. This includes heart disease (heart attack and stroke), adrenal issues (which can affect energy levels), infertility, unwanted weight loss or weight gain, sleep disorders, and cognitive issues (note that these are all the important systems the thyroid helps regulate).

This is why it’s important to monitor your thyroid hormone levels with blood tests as you age. Hypothyroidism, and the potential issues that can come with the medications associated, is what I’ll focus on here.

Symptoms of Hypothyroidism

How Thyroid Medication Side Effects Can Affect Your Life - Thyroid%20Symptoms%20or%20Gut%20Symptoms 16%20x%209 Landscape L

Since your thyroid regulates so many important functions in your body, when it’s inflamed, a myriad of symptoms can pop up. I’ll only focus on hypothyroid (underactive thyroid) symptoms, but often (not always), a hyperthyroid issue creates the opposite problem of hypo-. For example, hypothyroidism can lead to weight gain while hyper- can lead to weight loss.

According to the National Institutes of Health (NIH), symptoms for hypothyroidism include:

  • Fatigue/tiredness
  • Weight gain/difficulty losing or maintaining weight
  • Difficulty in tolerating cold weather
  • Joint and muscle pain
  • Irregular periods/excessively heavy flow
  • Infertility or other fertility problems
  • Slowed heart rate
  • Depression

Since a lot of these symptoms can occur gradually — and in the absence of a thyroid issue — the list of concerns can creep in without you or your healthcare provider realizing you have a thyroid problem. This is another argument for regular testing as you age. 

These symptoms may also be related to other conditions (like gut imbalances) that are significantly more common than hypothyroidism. 

It’s important to note that some of these symptoms, when treated individually, may lead to the use of prescription and over-the-counter (OTC) medications that can interact with thyroid meds if you ultimately do begin taking them. Those with asterisks (*) in the list below need to be taken at least four hours away from a thyroid med. Here are the most common drugs with potential drug interactions with levothyroxine (see the full list by following the reference link) [6]:

  • Estrogen-containing contraceptives (including birth control pills and ring)
  • Estrogens (hormone replacement therapy)
  • Antacids, namely calcium carbonate* (active ingredient in TUMS), aluminum, or magnesium (active ingredient in Maalox and Mylanta)
  • NSAIDs (fenamates, phenylbutazone, salicylates)
  • Dopamine agonists
  • Tricyclic antidepressants
  • Selective serotonin reuptake inhibitors (SSRIs)
  • Diazepam (Valium)
  • Lithium
  • Glucocorticoids
  • Ferrous sulfate* (iron)
  • Iodide
  • Sulfonamides
  • Cholestyramine*
  • Colestipol*
  • Coumarin derivatives
  • Warfarin
  • Antidiabetic drugs
  • Insulin
  • Cardiac glycosides
  • Cytokines (interferon-alpha, interleukin-2)
  • Growth hormones (somatrem, somatropin)

Always take levothyroxine on an empty stomach, and always seek medical advice from your doctor with regard to the meds you’re taking before starting a new one. This way, you can be aware of both potential side effects and contraindications (unwanted drug interactions).

Potential Thyroid Medication Side Effects

Woman checking her hair using a magnifying glass

All drugs have potential side effects, some more serious than others. While levothyroxine tends to have rare serious side effects when used properly, it’s important to know all of the potential thyroid medication side effects. 

Many of these side effects can arise when hypothyroidism is being overtreated, which is the big reason I want you to be aware of them. In short, adding in thyroid hormone when little or none is needed can create symptoms of hyperthyroidism and leave the patient worse off than how they started. Thyroid hormone replacement therapy isn’t something to be taken lightly or prescribed without a thorough assessment of blood work and other potentially confounding health issues. 

Potential negative thyroid medication side effects that are specific to levothyroxine include:

Body SystemSide Effects [6, 7 Trusted SourcePubMedGo to source, 8 Trusted SourcePubMedGo to source]
CardiovascularAngina pectoris (chest pain)
Tachycardia (rapid heart rate)
Arrhythmia (irregular heartbeat)
Palpitations (short-lived arrhythmia, heart racing)
Myocardial infarction (heart attack)
Atrial fibrillation
Increased/high blood pressure
Heart failure
Cardiac arrest
Central nervous systemAnxiety/nervousness
Insomnia (advised to take levothyroxine in the morning)
Emotional lability
GastrointestinalWeight loss
Weight gain
Increased appetite
Emesis (vomiting)
Abdominal cramps
SkinSkin rash/flushing
Alopecia (hair loss)
Diaphoresis (excessive sweating)
Dry skin
Menstrual irregularities
Decreased bone mineral density (secondary to TSH suppression)
ReproductiveImpaired fertility
LiverIncreased liver enzymes
Immunoallergic hepatitis 
Muscle weakness
Extreme fatigue
Pain in arms, jaw, back, or neck
RespiratoryDyspnea (shortness of breath)
Heat intolerance

While our clinical practice sees the overtreatment of hypothyroidism on (at least) a weekly basis, many studies show that overtreatment with a drug like levothyroxine is unlikely to be severely detrimental [9 Trusted SourcePubMedGo to source, 10 Trusted SourcePubMedGo to source, 11 Trusted SourcePubMedGo to source, 12 Trusted SourcePubMedGo to source].

This is a good thing, because it means your risk of serious side effects is still low. But the real issue may be a bit more complicated. For those who don’t actually require thyroid medication and who continue to experience symptoms that they may think are being caused by their thyroid, true underlying conditions can go unnoticed, and chronic symptoms can persist for years. 

Should You Be Taking Thyroid Medication?

Serious doctor talking to her patient

So how do you know if you should be taking thyroid medicine? I mentioned blood work, and that really is the place to start. You need to know your baseline before taking any steps to address the symptoms that are leading you to believe that you have thyroid disease.

To determine whether or not you have optimal thyroid levels, you should be asking for blood work to look at the following information:

  • TSH (thyroid stimulating hormone)
  • Free T4 (thyroxine)
  • Free T3 (triiodothyronine)
  • Thyroid antibodies (I won’t dig into these in this article, but read this for more detailed info, especially if you’re pregnant or planning on becoming pregnant)

In addition to blood tests, you can also ask for a thyroid ultrasound, which can identify nodules and may be used as a diagnostic predictor.


Your TSH is produced in the pituitary gland. A healthy range of TSH for an untreated patient not taking thyroid meds is 0.45-4.5 IU/mL [13 Trusted SourcePubMedGo to source]. This range can change if you’re pregnant or over 60 years old. If you’re taking levothyroxine, your level should be below 2.5 IU/mL [14].

If this number is too high, it could mean that your thyroid isn’t sufficiently utilizing TSH to create T4.

Free T4

T4 can be either free (available to use) or bound (bound to a protein and unusable). The ideal range for free T4 is 0.82-1.77 ng/dL. A number below this range (especially when paired with high TSH) indicates hypothyroidism, while a number above it (especially when paired with low TSH) indicates hyperthyroidism [15 Trusted SourcePubMedGo to source].

TSHFree T4Diagnosis
normal (0.35-4.5 mIU/L) [15 Trusted SourcePubMedGo to source]normal (0.8-1.8 ng/dL) [15 Trusted SourcePubMedGo to source, 17 Trusted SourcePubMedGo to source]Euthyroidism (Normal thyroid) [15 Trusted SourcePubMedGo to source]
higher end of normal range (2.4 – 4.5 mIU/L) lower end of normal range (0.8 – 1.3 ng/dL)“Sluggish” thyroid (“Suboptimal half” of the normal range)
somewhat high (4.5-8 mIU/L) [15 Trusted SourcePubMedGo to source]normal (0.8-1.8 ng/dL) [15 Trusted SourcePubMedGo to source, 17 Trusted SourcePubMedGo to source]Subclinical hypothyroidism [15 Trusted SourcePubMedGo to source]
high (≥ 8.0 mIU/L) [15 Trusted SourcePubMedGo to source]low (< 0.8 ng/dL) [15 Trusted SourcePubMedGo to source, 17 Trusted SourcePubMedGo to source]Overt hypothyroidism [15 Trusted SourcePubMedGo to source]

Free T3

T3 can be either free form (active and available for use) or reverse form (inactive). The ideal range for free T3 is 2.0-4.4 pg/mL. Measuring T3 can give you some good information about your health, but it will not help you diagnose a thyroid disease. Rather, low levels of free T3 and high levels of reverse T3 indicate inflammation, potential digestive issues, and signs of stress. 

There’s a synthetic T3 drug called Liothyronine, but there’s not strong evidence to indicate that it’s actually helpful in treating hypothyroidism, and it comes with its own list of side effects [16 Trusted SourcePubMedGo to source]. Rather, it makes more sense to address gut health in the case of low T3, which I’ll get into in the next section.

If, after looking over these numbers, you find that you might be in need of thyroid medication, then work with your doctor to come up with a good plan. To help you get started, here’s more information on how to find your ideal thyroid medication.

Subclinical Hypothyroidism and “Sluggish” Thyroid

Thyroid medication side effects

Now that you know healthy ranges of the two hormones most integral to helping you understand the health of your thyroid (TSH and free T4), in addition to having a better understanding of the role of T3 in diagnostics, what if your numbers don’t add up to something conclusive? 

Subclinical hypothyroidism is when your TSH levels are high but your free T4 is normal. This low-level issue doesn’t need to be treated by prescription drugs, and doing so could lead to at least one thyroid medication side effect [18 Trusted SourcePubMedGo to source]. In many cases, high levels of TSH can resolve on their own over time, especially if you take measures to get more sleep, reduce your stress, and improve your digestive health.

Some practitioners go a step even further, considering individuals with normal T4 and normal TSH levels to need medication if their levels are in the “suboptimal half” of the normal range. This is referred to as “sluggish thyroid”, and should absolutely not be treated with medication.

The Bottom Line

Woman touching her neck

Thyroid medication side effects are rare but often occur when a patient is overmedicated for subclinical hypothyroidism or “sluggish thyroid”. In a case like this, the meds not only create more problems than they solve, but they also may be covering up another problem, like gut health issues. You might find that resolving your gut health solves your subclinical thyroid hormone levels. You might also find that you have hypothyroidism that does need to be treated with prescription meds. The treatment simply needs to match the actual health challenge.

For a comprehensive look at your thyroid and gut health, reach out to our clinic to book an appointment.

➕ References
  1. Thyrolar (liotrix) dosing, indications, interactions, adverse effects, and more [Internet]. Available from:
  2. Burgos N, Toloza FJK, Singh Ospina NM, Brito JP, Salloum RG, Hassett LC, et al. Clinical Outcomes After Discontinuation of Thyroid Hormone Replacement: A Systematic Review and Meta-Analysis. Thyroid. 2021 May;31(5):740–51. DOI: 10.1089/thy.2020.0679. PMID: 33161885. PMCID: PMC8110016. Trusted SourcePubMedGo to source
  3. Livadas S, Bothou C, Androulakis I, Boniakos A, Angelopoulos N, Duntas L. Levothyroxine replacement therapy and overuse: A timely diagnostic approach. Thyroid. 2018 Nov 30; DOI: 10.1089/thy.2018.0014. PMID: 30351232. Trusted SourcePubMedGo to source
  4. SWEENEY LB, STEWART C, GAITONDE DY. Thyroiditis: An Integrated Approach – American Family Physician. Am Fam Physician. 2014 Sep 15;90(6):389–96.
  5. Vanderpump MPJ. The epidemiology of thyroid disease. Br Med Bull. 2011;99:39–51. DOI: 10.1093/bmb/ldr030. PMID: 21893493. Trusted SourcePubMedGo to source
  6. SYNTHROID®. 2005 Aug; Available from:
  7. Eghtedari B, Correa R. Levothyroxine. In: StatPearls. Treasure Island (FL): StatPearls Publishing; 2021. PMID: 30969630. Trusted SourcePubMedGo to source
  8. Hennessey JV, Malabanan AO, Haugen BR, Levy EG. Adverse event reporting in patients treated with levothyroxine: results of the pharmacovigilance task force survey of the american thyroid association, american association of clinical endocrinologists, and the endocrine society. Endocr Pract. 2010 Jun;16(3):357–70. DOI: 10.4158/EP0362.OR. PMID: 20551006. Trusted SourcePubMedGo to source
  9. Stott DJ, Rodondi N, Kearney PM, Ford I, Westendorp RGJ, Mooijaart SP, et al. Thyroid Hormone Therapy for Older Adults with Subclinical Hypothyroidism. N Engl J Med. 2017 Jun 29;376(26):2534–44. DOI: 10.1056/NEJMoa1603825. PMID: 28402245. Trusted SourcePubMedGo to source
  10. Mooijaart SP, Du Puy RS, Stott DJ, Kearney PM, Rodondi N, Westendorp RGJ, et al. Association Between Levothyroxine Treatment and Thyroid-Related Symptoms Among Adults Aged 80 Years and Older With Subclinical Hypothyroidism. JAMA. 2019 Nov 26;322(20):1977–86. DOI: 10.1001/jama.2019.17274. PMID: 31664429. PMCID: PMC6822162. Trusted SourcePubMedGo to source
  11. Gencer B, Moutzouri E, Blum MR, Feller M, Collet T-H, Delgiovane C, et al. The impact of levothyroxine on cardiac function in older adults with mild subclinical hypothyroidism: A randomized clinical trial. Am J Med. 2020 Jul;133(7):848-856.e5. DOI: 10.1016/j.amjmed.2020.01.018. PMID: 32171774. Trusted SourcePubMedGo to source
  12. Jabbar A, Ingoe L, Junejo S, Carey P, Addison C, Thomas H, et al. Effect of levothyroxine on left ventricular ejection fraction in patients with subclinical hypothyroidism and acute myocardial infarction: A randomized clinical trial. JAMA. 2020 Jul 21;324(3):249–58. DOI: 10.1001/jama.2020.9389. PMID: 32692386. Trusted SourcePubMedGo to source
  13. Thayakaran R, Adderley NJ, Sainsbury C, Torlinska B, Boelaert K, Šumilo D, et al. Thyroid replacement therapy, thyroid stimulating hormone concentrations, and long term health outcomes in patients with hypothyroidism: longitudinal study. BMJ. 2019 Sep 3;366:l4892. DOI: 10.1136/bmj.l4892. PMID: 31481394. PMCID: PMC6719286. Trusted SourcePubMedGo to source
  14. Q and A: TSH (thyroid stimulating hormone) | American Thyroid Association [Internet]. Available from:
  15. Sheehan MT. Biochemical Testing of the Thyroid: TSH is the Best and, Oftentimes, Only Test Needed – A Review for Primary Care. Clin Med Res. 2016 Jun;14(2):83–92. DOI: 10.3121/cmr.2016.1309. PMID: 27231117. PMCID: PMC5321289. Trusted SourcePubMedGo to source
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