Hypothyroidism Symptoms: 12 Signs of an Underactive Thyroid and How It Is Treated
Written by Cherlie Joseph, MSN, FNP-BC · Medically reviewed by Naurah Gaspard, DNP, FNP-C, FNP-BC · Updated November 2026
Hypothyroidism means your thyroid gland is not making enough thyroid hormone, so your body's systems slow down. Common symptoms are tiredness, weight gain, feeling cold, constipation, dry skin, thinning hair and heavy or irregular periods. A TSH blood test confirms it, and most people are treated with a daily levothyroxine pill.
In this guide
What hypothyroidism is and who gets it
Your thyroid is a small, butterfly-shaped gland in the front of your neck. Its hormones set the pace for your metabolism, heart rate, digestion, body temperature and more. When it underproduces, everything runs a little slower.
In the United States, the most common cause is Hashimoto's disease, an autoimmune condition in which the immune system gradually damages the thyroid. Other causes include thyroid surgery, radioactive iodine treatment, radiation to the neck, inflammation after pregnancy (postpartum thyroiditis) and certain medicines such as lithium and amiodarone. Women are much more likely than men to develop it, and risk rises after age 60 and with a family history of thyroid disease or other autoimmune conditions like type 1 diabetes or celiac disease.
12 common symptoms of an underactive thyroid
Symptoms come on slowly over months or years, so many people blame stress, aging or a busy life. Watch for:
- Tiredness that sleep does not fix
- Weight gain or trouble losing weight
- Feeling cold when others are comfortable
- Constipation
- Dry skin
- Thinning hair or brittle nails
- Muscle aches, stiffness or weakness
- Joint pain
- Heavier or irregular periods, or trouble getting pregnant
- Low mood or depression
- Brain fog and poor memory
- A slow heart rate, puffy face or a hoarse voice
Some people also notice a swollen neck (goiter). Many of these symptoms overlap with iron deficiency, depression, sleep apnea and perimenopause, which is why a blood test matters.
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The first test is TSH (thyroid-stimulating hormone). When your thyroid is underactive, your pituitary gland raises TSH to push it harder, so a high TSH usually means low thyroid function. Your provider will often add a free T4 and sometimes TPO antibodies to look for Hashimoto's.
| Result pattern | What it usually means |
|---|---|
| High TSH, low free T4 | Overt hypothyroidism, usually treated |
| High TSH, normal free T4 | Subclinical (mild) hypothyroidism; often rechecked first |
| Normal TSH | Thyroid is unlikely to be the cause of symptoms |
Reference ranges vary by lab, and a single mildly high TSH is often repeated in 6 to 12 weeks because illness, recent iodine exposure and biotin supplements can skew results. Stop biotin (often in hair, skin and nail vitamins) a few days before your test if your provider agrees.
Treatment: levothyroxine and what to expect
Most people take levothyroxine, a synthetic form of the T4 hormone your thyroid normally makes. It is an inexpensive generic for most people, and it is usually a lifelong medicine.
- Take it the same way every day, usually on an empty stomach with water, 30 to 60 minutes before breakfast, or as your label directs.
- Space it from calcium, iron, antacids and some cholesterol medicines by about 4 hours, since they block absorption.
- Expect gradual improvement. Energy often improves over a few weeks, but it takes about 6 to 8 weeks for TSH to settle after a dose change, so labs are rechecked then.
- Once stable, most people check TSH every 6 to 12 months, and more often in pregnancy.
- Too high a dose can cause a racing heart, anxiety, sweating or trouble sleeping. Tell your provider if you notice these.
If you are pregnant or planning pregnancy, contact your provider right away. Thyroid hormone needs usually rise early in pregnancy, and the dose often has to be adjusted quickly.
Getting thyroid care online in Florida
At OurTopClinic, a nurse practitioner licensed in your state can review your symptoms, order a TSH and free T4 at a nearby lab, and renew levothyroxine for people with a known diagnosis when recent labs support it. We do not promise a prescription; your provider decides after reviewing your history. A thyroid nodule, a quickly growing goiter or pregnancy with thyroid disease usually needs in-person or specialist care, and we will help you find it.
Get in-person care or call 911 if you have:
- Extreme drowsiness, confusion or trouble staying awake
- A very slow heartbeat, fainting or feeling very cold with swelling of the face or legs
- Trouble breathing or swallowing, or a neck lump that is growing quickly
- Chest pain or a racing, irregular heartbeat after starting or changing thyroid medicine
Frequently asked questions
What are the first signs of hypothyroidism in women?
Early signs often include tiredness, feeling cold, weight gain, constipation, dry skin, thinning hair and periods that become heavier or irregular. Because these are easy to overlook, a TSH blood test is the best way to check.
Can hypothyroidism go away?
Hashimoto's disease is usually permanent and needs lifelong treatment. Some types, such as postpartum thyroiditis or thyroiditis after a viral illness, can be temporary and may resolve within months.
Does levothyroxine cause weight loss?
Levothyroxine replaces missing hormone, which can help with water retention and modest weight gain caused by an underactive thyroid. It is not a weight loss medicine, and taking more than you need is unsafe.
Sources
Keep reading
- Hyperthyroidism Symptoms: Signs of an Overactive Thyroid
- Hair Loss in Women: Common Causes
- High Cholesterol Explained
- Browse all conditions and treatments A to Z
Need your levothyroxine refilled?
$79 refill review by a nurse practitioner licensed in your state. Adults 18+ in FL, NM, OR and WA.
Request a medication refill →
Cherlie Joseph, MSN, FNP-BC
Board-certified family nurse practitioner licensed in Florida, caring for adults online at OurTopClinic. Meet our providers.
This article is for general education and is not a substitute for medical advice. Treatment, including any prescription, is decided by a licensed provider after reviewing your health history. OurTopClinic is not for emergencies; if you have a medical emergency, call 911. OurTopClinic serves adults located in Florida, New Mexico, Oregon and Washington. Learn more at ourtopclinic.com.
