Synthroid Often Overprescribed in Patients with Subclinical Hypothyroidism: Study

According to the findings of a new study, many doctors overprescribe thyroid hormone replacement drugs, such as Synthroid, giving the medications to patients with less serious cases of hypothyroidism.

Yale and Mayo Clinic researchers warn doctors are overdiagnosing patients for hypothyroidism, when they may not actually have the condition or have extremely mild cases, known as subclinical, according to findings published this week in the journal JAMA Internal Medicine.

Researchers analyzed national data for commercially insured patients and Medicare Advantage enrollees from 2008 to 2018, including nearly 111,000 adults filled new prescriptions for thyroid medications like Synthroid, Levoxyl, and Tirosint.

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Synthroid, Tirosint, and Levoxyl are brand name versions of levothyroxine; a synthetic drug prescribed by doctors to mimic and replace natural hormones created by the thyroid gland. These hormones help with nearly every function in the human body including the production of other hormones, metabolism regulation, temperature regulation, and energy production.

Patients are prescribed these drugs to replace the hormones when the thyroid is not functioning, as with hypothyroidism, or when the thyroid must be removed due to cancer or other concerns.

Levothyroxine Overprescription

Researchers warn drugs like Synthroid are commonly overprescribed for many patients with subclinical hypothyroidism.

Across the ten-year study period, the number of people with normal thyroid function did not significantly change. In 2008, about 33% of patients had normal thyroid function, and by 2018 about 26% had normally functioning thyroid. The number of adults with clinical hypothyroidism diagnoses was 7% in 2008, and 8% in 2018. The number of adults with subclinical hypothyroidism was 59% in 2008, and 66% in 2018. However, about 61% of patients given new prescriptions of Synthroid had subclinical hypothyroidism, which means they could not be considered as having hypothyroidism. Similarly, 30% of patients with lab work indicating clear subclinical hypothyroidism were started on drugs like Synthroid anyway.

Subclinical hypothyroidism is when an adult has elevated thyrotropin levels, but the levels are less than 10 mIU/L and normal free thyroxine levels. This indicates the thyroid may not be functioning at its peak, but it is not functioning at a level considered a concern, or which warrants medication. Research indicates there is no clinically relevant benefit to giving Synthroid to patients who do not have a clear hypothyroidism diagnosis. It does not change their quality of life or thyroid-related symptoms.

The average thyrotropin level during the study period was about 5.8 mIU/L in 2008 and 5.3 mIU/L in 2018; not a significant change.

Levothyroxine is one of the most commonly prescribed drugs in the US, approximately 7% of the population is estimated to have an active prescription.

In the new study, roughly 60% of patients who were given new prescriptions for Synthroid or Levoxyl got them from a primary care doctor. Only about 11% received the prescriptions from an endocrinologist, a doctor trained to treat conditions effecting the endocrine system and hormones.

Current clinical guidelines recommend against starting Synthroid treatment for subclinical hypothyroidism.

Long-term Synthroid use has been linked to increased risk of cardiovascular disease, cardiac dysrhythmias, osteoporosis, and bone fractures. This puts patients who are being treated with the drugs, but don’t necessarily need them, at increased risk of health side effects.

“Frequent initiation of levothyroxine in these patients is at odds with evidence demonstrating no significant association of levothyroxine replacement with measures of health-related quality of life, thyroid-related symptoms, depressive symptoms, fatigue, or cognitive function,” the researchers wrote.


  • claireOctober 18, 2021 at 6:05 pm

    I have been talking Levothyroxin for 15 years,I have been having horrible side effects the whole time.Now I'm off it I'm fine.I want justice

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