What happens if you overtreat with Synthroid (levothyroxine)?

From the Guidelines

Overtreatment with Synthroid can lead to serious complications, including osteoporosis, fractures, abnormal cardiac output, and ventricular hypertrophy, emphasizing the need for careful dosing and regular monitoring of thyroid levels. The potential harms of overtreatment are a significant concern, as they can introduce opportunity costs and lead to a focus on certain areas of health at the expense of other conditions or care needs that are of higher priority for the patient's overall well-being 1. Some common signs of Synthroid overtreatment include:

• Rapid or irregular heartbeat
• Nervousness, anxiety, irritability
• Tremors, excessive sweating, heat intolerance
• Weight loss despite increased appetite
• Difficulty sleeping, muscle weakness
• Frequent bowel movements More serious complications can develop with prolonged overtreatment, including heart problems like atrial fibrillation, bone loss leading to osteoporosis, and rarely, thyroid storm (a life-threatening condition) 1. If you suspect Synthroid overtreatment, it is crucial to contact your healthcare provider immediately rather than adjusting your dose yourself, as they will likely order thyroid function tests to check your TSH and T4 levels and may reduce your Synthroid dosage accordingly. Regular monitoring of thyroid levels, typically every 6-12 months once stable, is essential to prevent overtreatment, as thyroid hormone needs can change over time due to aging, weight changes, other medications, or changes in health status.

From the FDA Drug Label

Levothyroxine sodium tablets has a narrow therapeutic index. Overtreatment or undertreatment with levothyroxine sodium tablets may have negative effects on growth and development, cardiovascular function, bone metabolism, reproductive function, cognitive function, gastrointestinal function, and glucose and lipid metabolism in adult or pediatric patients Over-treatment with levothyroxine may cause an increase in heart rate, cardiac wall thickness, and cardiac contractility and may precipitate angina or arrhythmias, particularly in patients with cardiovascular disease and in elderly patients

Overtreatment with levothyroxine sodium may lead to:

• Negative effects on:
  • Growth and development
  • Cardiovascular function
  • Bone metabolism
  • Reproductive function
  • Cognitive function
  • Gastrointestinal function
  • Glucose and lipid metabolism
• Increased heart rate
• Cardiac wall thickness
• Cardiac contractility
• Precipitation of angina or arrhythmias, particularly in patients with cardiovascular disease and in elderly patients 2

From the Research

Over-Treatment with Synthroid

• Over-treatment with Synthroid (levothyroxine) can lead to hyperthyroidism, a condition where the thyroid gland produces excess thyroid hormones 3, 4, 5.
• Hyperthyroidism can cause a range of symptoms, including anxiety, insomnia, palpitations, unintentional weight loss, diarrhea, and heat intolerance 3, 4.
• If left untreated, hyperthyroidism can lead to more serious health problems, such as cardiac arrhythmias, heart failure, osteoporosis, and adverse pregnancy outcomes 3.
• Treatment for hyperthyroidism typically involves antithyroid medications, radioactive iodine ablation, or surgery 3, 4, 5.
• In patients receiving long-term suppressive therapy with levothyroxine, beta-blockade can improve the quality of life by reducing symptoms of hyperthyroidism, such as palpitations and increased heart rate 6.

Risks of Over-Treatment

• Over-treatment with Synthroid can increase the risk of atrial fibrillation and osteoporosis, particularly in patients with subclinical hyperthyroidism 5.
• Thyroid stimulating hormone levels below the reference range should be avoided, as they can lead to adverse health outcomes 5.
• Patients with a history of thyroid disease or those taking levothyroxine should be closely monitored to avoid over-treatment and minimize the risk of hyperthyroidism 3, 4, 5.

Management of Hyperthyroidism

• The management of hyperthyroidism requires a patient-centered approach, taking into account the underlying pathology, age, sex, patient preference, and availability of expert thyroid surgical care 5.
• Treatment options for hyperthyroidism should be individualized, and patients should be closely monitored to avoid over-treatment and minimize the risk of adverse health outcomes 3, 4, 5.