Symptoms of Excessive Levothyroxine Intake
Excessive levothyroxine intake can cause anxiousness along with numerous other symptoms including arrhythmias, myocardial infarction, dyspnea, muscle spasm, headache, nervousness, irritability, insomnia, tremors, muscle weakness, increased appetite, weight loss, diarrhea, heat intolerance, menstrual irregularities, and skin rash. 1
Common Symptoms of Levothyroxine Overdose
Excessive levothyroxine leads to hyperthyroidism with the following manifestations:
Cardiovascular Symptoms
- Palpitations
- Tachycardia
- Arrhythmias (potentially serious)
- Increased blood pressure
- Myocardial infarction (in severe cases)
- Heart failure (in prolonged cases)
Neurological and Psychiatric Symptoms
- Anxiety
- Nervousness
- Irritability
- Insomnia
- Tremors
- Headache
- Cognitive impairment (confusion, disorientation)
- In severe overdose: cerebral embolism, seizures, coma 1
Gastrointestinal Symptoms
- Increased appetite
- Weight loss (despite increased appetite)
- Diarrhea
- Nausea
Musculoskeletal Symptoms
- Muscle weakness
- Muscle spasms
- Bone demineralization (with long-term excess) 2
Other Symptoms
- Heat intolerance
- Excessive sweating
- Menstrual irregularities
- Skin rash
- Fatigue
- Poor concentration
- Dyspnea (shortness of breath) 1, 3
Severity and Presentation
The FDA drug label notes that symptoms may not be evident immediately and can appear several days after ingestion of excess levothyroxine 1. The severity of symptoms correlates with the degree of thyroid hormone excess and duration of exposure.
High-Risk Groups
Certain populations are particularly vulnerable to adverse effects from excessive levothyroxine:
- Elderly patients
- Those with pre-existing cardiac conditions
- Patients with untreated adrenal insufficiency
- Individuals with hyperthyroidism 2
Management of Overdose
For suspected overdose:
- Reduce levothyroxine dosage or temporarily discontinue
- Initiate appropriate supportive treatment based on medical status
- Contact National Poison Control Center (1-800-222-1222) for current management guidance 1
Monitoring Considerations
Regular monitoring of thyroid function tests is essential to prevent overdosage:
- TSH and free T4 should be monitored every 6-12 months for stable patients
- More frequent monitoring (every 3-6 months) for patients with recent dose adjustments 2
Common Pitfalls
Patient Requests: Nearly half of physicians report that patient requests for tests and treatments are barriers to appropriate thyroid hormone management 4. Patients may request dose adjustments based on symptoms even when biochemically euthyroid.
Biotin Interference: Biotin supplements can interfere with thyroid function test results, causing either under or overestimation 2.
Medication Interactions: Certain medications can affect levothyroxine absorption or metabolism, potentially leading to overdosage symptoms.
Recognizing the full spectrum of symptoms associated with excessive levothyroxine is crucial for prompt diagnosis and management to prevent serious complications.