When dosed correctly, Armour Thyroid does not cause side effects because it replaces hormones that occur naturally in the body. However, if you do experience side effects while taking Armour Thyroid, it may mean that your dose is too high. Tell your doctor if you are experiencing any of the following adverse effects: Abdominal cramps, Alopecia, Ataxia, Cardiac arrhythmia, Chest pain, Constipation, Diaphoresis, Diarrhea, Dyspnea, Fever, Headache, Heat Intolerance, Increased appetite, Insomnia, Menstrual disease, Myalgia, Nervousness, Palpitations, Tachycardia, Tremor, Vomiting, Weight loss