--- title: "Underactive thyroid (hypothyroidism): Symptoms & Treatment" description: "A plain-English guide to an underactive thyroid — symptoms, diagnosis and treatment." url: https://healthanswers.co.uk/conditions/underactive-thyroid/ robots: noindex --- # Underactive thyroid (hypothyroidism): Symptoms & Treatment Health A–Z A plain-English guide to an underactive thyroid — symptoms, diagnosis and treatment. Written by HealthAnswers editorial team Medically reviewed by [HealthAnswers UK doctor review panel](https://healthanswers.co.uk/our-doctors/) Reviewed 3 July 2026 ## Quick answer What is underactive thyroid? An underactive thyroid (hypothyroidism) is when the thyroid gland does not produce enough thyroid hormone. This can cause tiredness, weight gain, feeling cold and low mood. It is diagnosed with a blood test and is usually treated effectively with a daily hormone replacement tablet. ## Who is this page for? This page is for people in the UK who want a plain-English overview of Underactive thyroid (hypothyroidism), including when to seek help and what NHS care usually involves. It explains general information, not what is wrong with you personally. ## Who should skip this page? Skip this page if you need a diagnosis, a prescription, or emergency care. It cannot replace a GP, pharmacist, NHS 111 or 999. If you are in immediate danger, call 999; for urgent advice that is not life-threatening, call 111 in England, Scotland or Wales, or use your GP out-of-hours service in Northern Ireland. On this page 5 sections ## Key facts about underactive thyroid - An underactive thyroid means too little thyroid hormone is produced. - Common symptoms include tiredness, weight gain and feeling cold. - It is diagnosed with a simple blood test. - It is usually treated successfully with a daily replacement tablet. ## What is an underactive thyroid? The thyroid is a small gland in the neck that produces hormones controlling how your body uses energy. An underactive thyroid, or hypothyroidism, is when it does not make enough of these hormones. This slows down many body processes and can cause a range of symptoms. It is a common condition, particularly in women and as people get older. ## Symptoms Symptoms usually develop gradually and can be easy to miss. They may include: - tiredness and low energy - weight gain - feeling the cold - dry skin and hair - constipation - muscle aches - low mood and difficulty concentrating Because these symptoms are common and can have many causes, a blood test is needed to confirm whether the thyroid is responsible. ## How it is diagnosed An underactive thyroid is diagnosed with a blood test that measures thyroid hormone levels. If your GP suspects a thyroid problem from your symptoms, this simple test usually gives a clear answer. ## How it is treated Treatment is usually straightforward and effective. It involves taking a daily tablet of a hormone called levothyroxine, which replaces what the thyroid is not producing. Your GP will check your blood levels and adjust the dose until it is right for you. Once stabilised, most people feel substantially better. ## Living with an underactive thyroid For most people, treatment is lifelong but simple, with regular blood tests to keep the dose correct. With the right treatment, an underactive thyroid usually has little impact on daily life. ## ! When to see a GP about underactive thyroid See a GP if you have symptoms such as ongoing tiredness, unexplained weight gain, feeling the cold, dry skin or low mood, as these can have many causes and a blood test can check your thyroid. If you are already treated for an underactive thyroid, see your GP if symptoms return or change, as your dose may need adjusting. ## Common questions about underactive thyroid What are the symptoms of an underactive thyroid? Symptoms often develop slowly and can include tiredness, weight gain, feeling cold, dry skin and hair, constipation, muscle aches and low mood. Because these are common and non-specific, a blood test is needed to confirm the cause. What causes an underactive thyroid? The most common cause is the immune system attacking the thyroid gland. It can also follow some thyroid treatments or, less commonly, be linked to other factors. It is more common in women and becomes more likely with age. How is an underactive thyroid treated? It is usually treated with a daily tablet of a hormone called levothyroxine, which replaces the hormone the thyroid is not making. Most people feel much better once the right dose is found, and treatment is often lifelong. Do I need treatment for life? In most cases yes, but the medication simply replaces a hormone your body needs, and regular blood tests ensure your dose is right. Many people live completely normally once treated. ## Sources - [NHS — Underactive thyroid (hypothyroidism)](https://www.nhs.uk/conditions/underactive-thyroid-hypothyroidism/)