Levothyroxine

The exam loves the timing and lab-interval question: TSH is rechecked roughly 6–8 weeks after any dose change, so a stem about a patient who “feels no better after one week” is testing whether you’ll wrongly escalate — the right answer is reassure and wait, because the full effect takes weeks. Watch for over-replacement tells: tachycardia, palpitations, weight loss, heat intolerance, insomnia, and tremor mean the dose is too high (signs of hyperthyroidism/thyrotoxicosis), and a resting heart rate over 100 or new chest pain is a classic cue to hold and notify the provider. In older adults or cardiac patients, expect “start low, go slow” to avoid precipitating angina or arrhythmia.

Classic traps: don’t confuse the under-replaced patient (fatigue, cold intolerance, constipation, weight gain → raise the dose) with toxicity. Mind absorption pitfalls — separate from calcium, iron, and antacids by ~4 hours (PPIs may also blunt uptake, though the effect is less consistent). Memory hook: “T4 = TSH check, Take on an empty stomach, Tachycardia = too much.”