welche nebenwirkungen hat l-thyroxin — what are common causes?

L-Thyroxine (levothyroxine) is a thyroid hormone used to treat hypothyroidism. Most side effects result from over- or under-dosing. Overdose can cause palpitations, tachycardia, nervousness, tremor, insomnia, excessive sweating, weight loss, and diarrhea – resembling hyperthyroidism. Underdose may lead to fatigue, weight gain, cold intolerance, and constipation. True allergic reactions are rare. Common causes of side effects include incorrect dosage, too rapid dose escalation, drug interactions (e.g., with iron, calcium, antacids), or improper intake (on an empty stomach, 30 minutes before breakfast). Individual factors like malabsorption or genetic variants (e.g., in the MCT8 transporter) can also contribute. Importantly, L-thyroxine is a vital hormone; with correct dosing and adherence, side effects are uncommon. Regular TSH monitoring is essential. The evidence is based on clinical practice and guidelines, not on direct studies from the provided context.