Hypothyroidism: Symptoms and Causes of an Underactive Thyroid

You've been tired all the time lately, no matter how much you sleep, and you've put on a little weight without changing much about your routine. You're starting to wonder if something else is going on, something that diet and rest alone can't fix.

This article covers what happens when your thyroid doesn't make enough hormones, common causes of hypothyroidism, the symptoms to watch for, and when it's time to get your thyroid checked.

What Happens When Your Thyroid Doesn't Make Enough Hormone?

The thyroid is a small, butterfly-shaped gland in your neck that produces thyroid hormone, which helps regulate your metabolism, energy, and a long list of other body functions. Hypothyroidism happens when your thyroid gland doesn't make enough of that hormone to keep things running the way they should.

This is different from hyperthyroidism, also called overactive thyroid, which happens when the gland produces too much thyroid hormone instead.

Hypothyroidism is the most common thyroid disorder, and it tends to develop gradually, which is part of why the early signs of thyroid trouble are easy to chalk up to stress or just getting older.

A pituitary gland in your brain signals the thyroid through thyroid-stimulating hormone, or TSH, telling it how much hormone to release. When this signaling system is off, or when the thyroid gland itself isn't functioning properly, thyroid hormone levels drop, and that's when symptoms start to show up.

What Causes Hypothyroidism?

There are several causes of hypothyroidism, and figuring out which one applies to you helps shape the right treatment plan. The most common cause of hypothyroidism is an autoimmune condition called Hashimoto's disease, where the immune system attacks the thyroid gland, slowly reducing its ability to make hormones over time. Hashimoto's disease is an autoimmune condition that affects the thyroid and often runs in families.

Other things that can lead to hypothyroidism include thyroid surgery, where part or all of the thyroid gland is removed, and radiation therapy used to treat certain cancers, which can affect thyroid function as a side effect. Some people develop hypothyroidism after taking too much medication for hyperthyroidism, since correcting an overactive thyroid can sometimes tip things too far the other way.

Iodine plays a role too. Your thyroid needs iodine to make thyroid hormones, so both too little and too much iodine in your diet can contribute to thyroid dysfunction. In rarer cases, someone is born with no thyroid gland at all or with one that doesn't develop properly, a condition called congenital hypothyroidism. People born with hypothyroidism are typically identified through newborn screening, so it's caught early.

What Are the Symptoms of Hypothyroidism?

Symptoms of an underactive thyroid often develop slowly, which makes them easy to miss at first. Common symptoms include:

• Feeling tired or fatigued even with adequate sleep

• Unexplained weight gain

• Feeling unusually cold all the time

• Dry skin and thinning hair

• Constipation

• Muscle aches or joint pain

• Slowed heart rate or feeling sluggish overall

Hypothyroidism symptoms often develop gradually over months, making them easy to mistake for normal aging or everyday stress. Changes in mood, memory, or concentration can also be related and are worth discussing with your healthcare provider.

How Is Hypothyroidism Diagnosed and Treated?

If you suspect a thyroid issue, a doctor will typically start with thyroid blood tests to check your TSH levels and your thyroid hormone levels directly. Low levels of thyroid hormone paired with elevated TSH usually confirm hypothyroidism, though your doctor may run additional tests to confirm the underlying cause, especially if an autoimmune disease like Hashimoto's is suspected.

Treatment for hypothyroidism usually involves taking thyroid hormone medicine, typically a daily pill that replaces what your thyroid gland isn't producing on its own. Most people feel noticeably better within a few weeks of starting thyroid hormone replacement, though it can take some trial and error with your doctor to find the right dose. Periodic blood tests help make sure your levels stay in a healthy range over time, since needs can shift gradually.

Left untreated, hypothyroidism can lead to more serious problems, including heart issues, nerve damage, and complications during pregnancy. Hypothyroidism during pregnancy needs particular attention, since thyroid hormone plays an important role in a developing baby's growth, and untreated thyroid disease can affect both parent and child.

When Should You Get Your Thyroid Checked?

If you're noticing several of the warning signs of like persistent fatigue, weight gain you can't explain, feeling cold often, or changes in your skin and hair, it's worth bringing it up with a doctor rather than waiting to see if it resolves on its own. A simple blood test is usually all it takes to get a clearer picture of your thyroid function.

People with a family history of autoimmune disease or thyroid disorder, or anyone who's had thyroid surgery or radiation therapy in the past, may want to bring up thyroid issues even without obvious symptoms, since some thyroid imbalances develop quietly over time.

A telehealth visit can be a convenient way to start that conversation. You can describe what you've been noticing, go over your medical history with a provider, and get a referral for blood work without needing to schedule an in-person appointment first. Once your test results are available, many follow-up appointments can be done through virtual visits, making it easier to review your treatment plan and adjust your medication without an in-person appointment.

This blog is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult your doctor or a qualified healthcare provider with any questions you may have regarding a medical condition.