Persistent tiredness is one of the most common reasons people see a doctor — and one of the most commonly missed causes is an underactive thyroid (hypothyroidism). It develops slowly, its symptoms are easy to blame on stress or age, and yet it's simple to test for and very treatable.
What the thyroid does
The thyroid is a small, butterfly-shaped gland in the neck that sets your body's "pace" — metabolism, temperature, energy, even mood. When it makes too little hormone, everything slows down.
Signs of an underactive thyroid
- Tiredness and low energy that rest doesn't fix
- Weight gain despite no change in eating
- Feeling cold when others are comfortable
- Dry skin and hair, hair thinning
- Constipation
- Low mood or brain fog, poor concentration
- Heavier or irregular periods in women
- A slower heartbeat
Any one of these has many possible causes — but several together are worth a blood test.
Who is more likely to get it
Hypothyroidism is far more common in women, and risk rises with age. It's also more likely if you have a family history of thyroid disease, another autoimmune condition, or after pregnancy. In India, it is very common and often under-diagnosed.
The test is simple
A blood test for TSH (thyroid-stimulating hormone), often with T4, tells the story. A high TSH usually means the thyroid is underactive. Sometimes doctors add thyroid antibody tests to find the cause (the commonest is an autoimmune condition called Hashimoto's).
Treatment is straightforward — and lifelong for most
The standard treatment is a daily tablet of thyroid hormone (levothyroxine) that simply replaces what the gland isn't making. Taken correctly — usually on an empty stomach, with periodic blood tests to fine-tune the dose — most people feel like themselves again. It's safe and inexpensive, but it does need to be taken consistently, and the dose set by a doctor.
A note on the opposite problem
An overactive thyroid (hyperthyroidism) does the reverse — weight loss, a racing heart, anxiety, heat intolerance, tremor. If those are your symptoms, mention them: it's a different diagnosis and treatment.
When to see a doctor
Book a test if fatigue, weight change and feeling cold have crept up over weeks or months. Seek prompt care for a very slow heart rate with severe drowsiness or confusion, which is rare but serious.
Frequently asked questions
Can a thyroid problem cause weight gain? An underactive thyroid can cause modest weight gain and make losing weight harder. Treatment usually helps, but thyroid disease is rarely the sole cause of major weight gain.
Is thyroid medicine for life? For most people with an underactive thyroid, yes — but the dose is adjusted over time with blood tests. Don't stop without medical advice.
Which test checks the thyroid? A blood test — mainly TSH, often with T4, and sometimes antibodies to find the cause.
Wondering if your tiredness could be thyroid-related? Ask MedDroid's free AI — plain-language answers on symptoms and reports, in your language.
Learn more: Hypothyroidism — causes, symptoms & treatment
Written and medically reviewed by Dr. Sanjay Anbu, MBBS. General health information, not a diagnosis. In an emergency, call your local emergency number.