4 Dangers of Too Much Thyroid Medication and How to Prevent Them

dangers of too much thyroid medication: Doctor's hand holding a thyroid gland model and a stethoscope

Treating hypothyroidism with thyroid hormone medication, like levothyroxine sodium (Synthroid), is an effective treatment option for most patients. However, mounting research suggests that many patients are overusing thyroid medication, with potential consequences for their health. For patients taking thyroid hormone replacement, it’s important to understand the dangers of too much thyroid medication and how to know if you’re at risk.

In this article, we’ll cover the dangers of too much thyroid medication including overmedication, overprescribing T3, thyroid medication absorption changes, and overdose. We’ll also discuss how thyroid medication is only part of the solution for many thyroid patients. What’s not yet well understood by many practitioners is that improved gut health may be the missing puzzle piece for patients with stubborn thyroid symptoms.

Thyroid Gland Basics

Working with the adrenal gland and pituitary gland, the thyroid gland releases thyroid hormones into the bloodstream. These hormones regulate bodily functions, including:

  • Brain and nervous system function
  • Digestion
  • Energy production
  • Muscle and heart function
  • Body temperature
  • Bodyweight
  • Fertility

When the thyroid gland produces too much or too little thyroid hormone, multiple body systems are affected.


This condition occurs when an overactive thyroid gland produces excess thyroid hormones, speeding up the body’s metabolism. Common hyperthyroidism symptoms include: 

  • Weight loss 
  • Anxiety
  • Racing heart rate or palpitations 
  • Blood pressure changes 
  • Tremors
  • Insomnia
  • Osteoporosis 


Hypothyroidism occurs when an underactive thyroid gland doesn’t produce a sufficient amount of thyroid hormones, slowing down the body’s metabolism. Common hypothyroidism symptoms include:

  • Fatigue/tiredness  
  • Hair loss 
  • Weight gain
  • Depression
  • Brain fog 
  • High cholesterol
  • Headaches
  • Low libido
  • Osteoporosis
dangers of too much thyroid medication: Hypothyroid vs. Hyperthyroid Symptoms

Dangers of Too Much Thyroid Medication

If you are hypothyroid, a thyroid hormone replacement medication like levothyroxine (Synthroid, Tirosint, or Levoxyl) can help to restore proper thyroid function

Levothyroxine is sold under the brand names Tirosint, Synthroid, and Levoxyl. The FDA recommends taking levothyroxine in the morning on an empty stomach at least 30 minutes prior to eating. The FDA also recommends not taking levothyroxine with calcium, iodine, antacids, or other medications that could interfere with medication absorption [1].

If for any reason you take too much thyroid hormone medication, you may experience mild to severe symptoms of hyperthyroidism. Let’s take a look at some of the scenarios where this could happen.


dangers of too much thyroid medication: Thyroid gland model, stethoscope, and medicines

One of the more common dangers of too much thyroid medication is overmedication resulting from overdiagnosis.

Research has found that thyroid medication is highly overprescribed.

One study demonstrated that up to 60% of patients might be taking thyroid hormone replacement unnecessarily [2]. The study documented 291 patients taking Levothyroxine Sodium (Synthroid) who halted their medication for 6-8 weeks. It’s important to note that many of these patients had been taking thyroid medication for years but did not have apparent thyroid disease diagnostic indicators.

After halting medication, follow-up thyroid function tests showed that 60.8% of patients had thyroid-stimulating hormone results in the normal range. Essentially, their bodies were producing enough thyroid hormones and they did not require thyroid medication.

In another study conducted over nine years, 52,000 thyroid patients completed surveys regarding levothyroxine (Synthroid) use. Results showed a 30% increase in levothyroxine use over this time, suggesting a likely propensity toward overdiagnosis [3].

While both functional and conventional medical practitioners appear to over-diagnose hypothyroidism, this tends to be an area where conventional medical practitioners get it right more often than functional medicine practitioners. Some alternative practitioners apply very narrow, non-standard ranges to thyroid function blood test results. However, standard laboratory reference ranges for thyroid hormones are based on current research, and there is little evidence to support the practice of applying non-standard ranges.

If you’ve been taking thyroid hormone replacement, you’re likely familiar with low thyroid symptoms (hypothyroid). However, you may not immediately recognize the signs of hyperthyroidism that can result from overmedication. 

Common symptoms of overmedication of hypothyroidism include:

  • Insomnia
  • Feeling stressed
  • Anxiousness 
  • Irritability 
  • Racing heart rate
  • Hair loss  

These hyperthyroidism symptoms are similar to what you might experience during stressful times in your life. This can make it difficult to identify hyperthyroidism caused by too much thyroid medication. 

Over-Prescribing T3

Woman holding up a hand to her neck

Low T3 is a condition associated with inflammation, chronic illness, and poor nutrition [5]. Several functional medicine providers promote the view that combination thyroid medication — including both T3 (liothyronine) and T4 — is better than using T4 alone. But is this always true? Our clinical team recently reviewed the evidence for using combination T3/T4 therapy. We reviewed one meta-analysis and 16 randomized control trials. We could not find substantial evidence that combination T3/T4 therapy was more advantageous than standard T4 medication [4]. 

Additionally, overprescribing T3 can be harmful. We see a lot of patients who have been prescribed T3 when it wasn’t needed. This can increase fatigue/tiredness, a decline in mood, and impair sleep. Some patients have suffered with these symptoms for years, before coming to our center for functional medicine and learning they have been overmedicating with T3 .

Guidelines published by the American Thyroid Association and the American Association of Clinical Endocrinologists do not recommend combination T4/T3 therapy [6]. Practice guidelines for the European Thyroid Association recommend caution in prescribing combination T4/T3 therapy [7]. 

Rather than prescribing thyroid hormone replacement for low T3 levels, treating gut imbalances and nutritional deficiencies will likely provide more significant benefits for patients.

Improved Thyroid Medication Absorption

Poor gut health, including gut dysbiosis, low stomach acid, food sensitivities, and other gut conditions, can impair the absorption of standard thyroid hormone medication [8, 9, 10, 11]. 

When gut health improves, absorption of thyroid medication may improve. This can lead to overmedication and hyperthyroidism. 

Research shows how treating gut issues can affect the absorption of thyroid medication. Several studies found that gut infections, food sensitivities, low stomach acid, and other gut conditions can impair absorption of standard thyroid hormone medication [12, 13, 14, 15].

One study found 21% of patients could reduce their thyroid medication dose after treating H. pylori [16].

If you take thyroid medication and have taken steps to improve your gut health, it’s worth having your thyroid-stimulating hormone and thyroxine levels rechecked periodically to see if you need to adjust your thyroid medication dosage.


Research shows accidental overdose is most common in children and adolescents. However, it may intentionally occur in adults attempting weight loss or patients who present with suicidal ideations [17]. If you or someone you know is feeling suicidal or like inflicting self-harm, call the National Suicide Hotline at 800-273-8255.

When the body accumulates very high levels of thyroid hormone, overdose leading to serious side effects and fatality can occur. Typically, an overdose of thyroid medication progresses as follows:

  • Mild side effects typically appear 6-12 hours after ingestion.
  • Severe side effects can occur from 3-10 days after thyroid medication ingestion [17]. 
Mild side effects of thyroid medication overdose• Nervousness
• Insomnia
• Hand Tremors
• Tachycardia (rapid heart rate)
• Elevated body temperature
• Elevated blood pressure
• Diarrhea
Severe side effects of thyroid medication overdose• Coma
• Convulsions
• Acute psychosis (delusions and hallucinations)
• Irregular heart palpitations
• Chest pain

If caught early, ingestion of activated charcoal or cholestyramine can help prevent the thyroid medication from being absorbed into the gastrointestinal system.

Thyroid Hormone Testing

Thyroid gland model and a test tube with a blood specimen

If you suspect that your thyroid medication dose is off, it’s essential to request a follow-up blood test to check TSH (thyroid-stimulating hormone) and free T4 (thyroxine) levels.

Here are the lab reference ranges to keep in mind for optimizing your thyroid medication:

TSH levels

  • The standard lab reference range for thyroid-stimulating hormone (TSH) is 0.45−4.5 IU/mL [18].
  • The standard lab range may require adjustments if you are pregnant or over 60 years of age.
  • For hypothyroid patients who take thyroid hormone replacement, optimal levels of TSH may be below 2.5 IU/mL [19].

T4 (thyroxine) levels

  • The standard lab reference range for free T4 (thyroxine) is 0.82−1.77 ng/dL.
  • For hypothyroid patients who take thyroid hormone replacement, optimal T4 levels may be in the higher half of the lab range. However, research to support this is lacking.

Bottom Line

Thyroid medication is an effective treatment for hypothyroidism. However, it’s crucial for patients to understand that overmedication, overprescribing T3, improved thyroid medication absorption, and overdose are dangers of too much thyroid medication that need to be monitored. For some thyroid patients, medication is only part of the solution. 

Contact us today for more information on the dangers of too much thyroid medication and the steps you can take to improve your thyroid health. 


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