Hypothyroidism (Underactive Thyroid)

Hypothyroidism (underactive thyroid disease) is a condition that happens when your thyroid gland doesn’t make or release enough hormone into your bloodstream. As a result, your metabolism slows down. This can cause unintentional weight gain and make you feel exhausted all the time.

Although weight gain and fatigue aren’t specific to hypothyroidism, a simple blood test can help your healthcare provider check for this condition.

In general, hypothyroidism is very treatable. Most people can manage the condition with medication and regular follow-up visits with their endocrinologist.

Left untreated over long periods of time, hypothyroidism can become life-threatening. If you develop new symptoms, it’s important to get an evaluation.

Types of hypothyroidism

There are four main types of hypothyroidism:

• Primary hypothyroidism directly impacts your thyroid and causes it to make low levels of thyroid hormones. In turn, your pituitary gland makes more thyroid stimulating hormone (TSH). Autoimmune conditions like Hashimoto’s disease can cause it, or it can happen after thyroid gland surgery or radiation therapy. Primary hypothyroidism is the most common type.
• Secondary hypothyroidism occurs when you have an underactive pituitary gland (a pea-sized gland at the base of your brain). This rare type of hypothyroidism prevents your pituitary gland from sending TSH to your thyroid gland.
• Tertiary hypothyroidism happens when your hypothalamus (a structure in your brain that keeps your body in a stable state called homeostasis) doesn’t make enough thyrotropin-releasing hormone (TRH). As a result, your pituitary gland can’t make enough TSH.
• Subclinical hypothyroidism, also known as mild thyroid failure, happens when you have slightly elevated TSH levels, but all other thyroid hormone levels are within a typical range. Subclinical hypothyroidism usually goes away on its own in about three months.

How common is hypothyroidism?

Hypothyroidism can affect anyone. It’s most common among people assigned female at birth (AFAB) over age 60, particularly after menopause.