Before you begin your Armour Thyroid prescription, it’s important to understand the possible side effects, which include:HeadacheDiarrheaVomitingIrritabilityLeg crampsUnexpected weight lossChest painFeverHand tremorsSweatingTrouble sleepingChanges in appetiteAlso, at large doses, there’s the possibility for serious or life-threatening levels of thyroid toxicity. Always be sure to follow the dosage instructions given to you by your doctor, and seek immediate medical attention if any of these side effects become severe.