Symptoms of depression, such as low mood and lack of interest in relationships or activities you usually enjoy, are common among people with hypothyroidism. Therefore, hypothyroidism is often mistaken for depression. A healthcare provider can distinguish between the two conditions by testing for thyroid hormone levels. If they come back abnormal, then thyroid issues are likely the underlying cause of depressive symptoms. However, if the tests come back and thyroid hormone levels are normal, then your healthcare provider may suggest further assessment, including tests for depression.