Like all medicines, Armour Thyroid can cause side effects, although not everybody gets them. Potential side effects of Armour Thyroid include the following: heart palpitations, chest pains, difficulty in breathing, increased appetite, insomnia (sleeplessness), hair loss, skin flushing, fever and increased sweating, anxiety, stomach upsets and diarrhoea. Because Armour Thyroid contains extracts of animal thyroid glands, its also important to watch out for the signs of an allergic reaction, such as a rash, itching, wheezing, or a swelling on any part of the body especially the face or throat. If any of these are experienced and are troublesome please talk to your pharmacist or the prescribing doctor straight away.