Yes, thyroid disease can affect your mood — primarily causing either anxiety or depression. Generally, the more severe the thyroid disease, the more severe the mood changes.
If you have an overactive thyroid (hyperthyroidism), you may experience unusual nervousness, restlessness, anxiety and irritability. On the opposite end of the spectrum, if you have an underactive thyroid (hypothyroidism), you may experience mild to severe fatigue and depression.
Still, it's unlikely that emotional symptoms such as anxiety or depression would be the only evidence of thyroid disease. Thyroid disease is usually associated with signs and symptoms such as weight gain or loss, sensitivity to hot or cold, bowel movement changes, and menstrual irregularities.
Appropriate treatment — such as medication that blocks your body's ability to produce new thyroid hormone or replaces missing thyroid hormone — usually improves both emotional and physical symptoms caused by thyroid disease.