welche nebenwirkungen hat l-thyroxin — which blood markers matter?

L-Thyroxine (levothyroxine) is used to treat hypothyroidism. Most side effects stem from over- or under-dosing. Overdose can cause palpitations, tremor, insomnia, anxiety, sweating, diarrhea, and weight loss – resembling hyperthyroidism. Underdose leads to fatigue, sluggishness, cold intolerance, constipation, and weight gain. Key blood markers are TSH (thyroid-stimulating hormone) and free T4 (fT4). TSH is the most sensitive indicator: low TSH suggests overmedication, high TSH suggests undermedication. fT4 reflects the actual available thyroid hormone. In some cases, free T3 (fT3) is measured, especially when conversion issues are suspected. Important: Dosing must be managed by a physician; self-adjustment is dangerous. Drug interactions (e.g., iron, calcium, antacids) can affect absorption. Evidence is based on decades of clinical practice and guidelines. Caveat: Direct-to-consumer tests cannot replace professional diagnosis.