When dosed correctly, Nature-Thyroid does not cause any side effects. However, when the dose is too high, it can cause side effects which are similar to hyperthyroidism. Common adverse effects when the dose of Armour Thyroid is too high include: 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 Nature Throid [package insert]. Cave Creek, AZ: RLC Labs; 2003. Thyroid Hormones, December 2018. Retrieved May 2020.