The thyroid gland, located at the front of the neck, produces thyroid hormone, which is how the body controls its metabolism, or how the body uses energy.
As such, the thyroid gland and thyroid hormone are involved in converting food into energy, and are involved with elements of heart, muscle, and bone health.
When a person's thyroid produces hormone levels above normal, they're said to have hyperthyroidism (or an overactive thyroid gland).
By contrast, when a person's thyroid gland produces hormone levels below normal thyroid levels, that person is said to have hypothyroidism (or an underactive thyroid).
Many symptoms of an over-active and under-active thyroid gland are the same, including feeling tired or weak, and feeling moody, anxious, or depressed.
From there, symptoms of the two diverge, with above-normal thyroid levels producing symptoms of red, itchy, warm skin and more bowel movements than you're used to, while below-normal thyroid levels may produce symptoms of constipation, a problem handling cold weather, and trouble with memory and mental clarity.
In either case, there are treatments for both.
With many of these thyroid treatments, a person can easily restore and maintain normal thyroid levels.
If you believe you are experiencing symptoms of above or below normal thyroid levels, it is wise to speak with your doctor about it.
A simple physical exam with a blood test can help your doctor determine if what you're experiencing is hyper- or hypo- thyroidism, and if so, what the best course of treatment for you may be.