Hypothyroidism is when a person does not have enough thyroid hormone. It is also called an underactive thyroid. Symptoms include weight gain, dry skin, constipation, intolerance to the cold, mental fatigue, tiredness, slow heart rate, hair loss, and impaired memory. Treatment options for hypothyroidism include taking a thyroid hormone replacement, vitamin and nutritional supplements, yoga, herbal remedies, Ayurveda, and homoeopathy.