From the FDA Drug Label
Adverse reactions associated with levothyroxine sodium therapy are primarily those of hyperthyroidism due to therapeutic overdosage [see Warnings and Precautions (5), Overdosage Error! Hyperlink reference not valid.] They include the following: • General:fatigue, increased appetite, weight loss, heat intolerance, fever, excessive sweating • Central nervous system:headache, hyperactivity, nervousness, anxiety, irritability, emotional lability, insomnia • Musculoskeletal:tremors, muscle weakness, muscle spasm • Cardiovascular:palpitations, tachycardia, arrhythmias, increased pulse and blood pressure, heart failure, angina, myocardial infarction, cardiac arrest • Respiratory:dyspnea • Gastrointestinal:diarrhea, vomiting, abdominal cramps, elevations in liver function tests • Dermatologic:hair loss, flushing, rash • Endocrine:decreased bone mineral density • Reproductive:menstrual irregularities, impaired fertility Seizures have been reported rarely with the institution of levothyroxine therapy Adverse Reactions in Pediatric Patients Pseudotumor cerebri and slipped capital femoral epiphysis have been reported in pediatric patients receiving levothyroxine therapy Overtreatment may result in craniosynostosis in infants who have not undergone complete closure of the fontanelles, and in premature closure of the epiphyses in pediatric patients still experiencing growth with resultant compromised adult height. Hypersensitivity Reactions Hypersensitivity reactions to inactive ingredients have occurred in patients treated with thyroid hormone products These include urticaria, pruritus, skin rash, flushing, angioedema, various gastrointestinal symptoms (abdominal pain, nausea, vomiting and diarrhea), fever, arthralgia, serum sickness, and wheezing. Hypersensitivity to levothyroxine itself is not known to occur.
Thyroid abnormalities can cause muscle symptoms. The adverse reactions associated with levothyroxine sodium therapy include:
- Musculoskeletal symptoms such as tremors, muscle weakness, and muscle spasm. However, muscle fasciculations are not explicitly mentioned in the provided drug labels 1, 1, or 1. Therefore, no conclusion can be drawn about the specific relationship between thyroid abnormalities and muscle fasciculations.