The thyroid is a small, butterfly-shaped gland in the front of your neck. It releases hormones (mainly T4 and T3) that set the pace of your metabolism — how your body uses energy and regulates temperature, heart rate, digestion, and mood.
When the gland makes too little hormone, the result is hypothyroidism (an underactive thyroid); too much causes hyperthyroidism (an overactive thyroid). Thyroid problems are far more common in women and often appear in midlife, where their symptoms overlap with menopause.