Underactive Thyroid: Symptoms, Causes and How to Manage It

This subject is especially important to me because I also live with an underactive thyroid, medically known as hypothyroidism.

I understand the frustration of feeling cold when everyone else is comfortable. I understand what it's like to put on socks in warm weather because your body still feels freezing. I also remember crying and booking a GP appointment because my hair was shedding so heavily that I genuinely worried I was going bald.

At the time, I didn't realise that these different experiences could be connected.

This guide explains what the thyroid does, the difference between an underactive and overactive thyroid, the symptoms to look out for, available treatment and the everyday habits that may help you manage your wellbeing.

What is the thyroid?

The thyroid is a small, butterfly-shaped gland located at the front of your neck.

Although it is small, it produces hormones that influence many important processes within the body, including:

• Metabolism

• Energy levels

• Body temperature

• Heart rate

• Digestion

• Concentration

• Muscle function

• Skin and hair health

• Menstrual cycles

When your thyroid produces too little or too much thyroid hormone, many of these processes can be affected.

The two main thyroid conditions are:

• Hypothyroidism, also known as an underactive thyroid

• Hyperthyroidism, also known as an overactive thyroid

This guide covers both briefly but focuses mainly on an underactive thyroid because this is the condition I personally live with.

Underactive versus overactive thyroid: What is the difference?

Although both conditions affect the thyroid gland, their effects can be very different.

Underactive thyroid

An underactive thyroid does not produce enough thyroid hormones. This can cause many of the body's processes to slow down.

Common symptoms can include:

• Persistent tiredness

• Feeling cold more than usual

• Weight gain

• Difficulty concentrating

• Constipation

• Dry skin or hair

• Hair loss

• Low mood

• Heavy or irregular periods

Overactive thyroid

An overactive thyroid produces too much thyroid hormone, causing many of the body's processes to speed up.

Symptoms can include:

• Feeling unusually hot

• Increased sweating

• Unexplained weight loss

• Anxiety or irritability

• Difficulty sleeping

• Trembling hands

• Muscle weakness

• Diarrhoea

• A fast or irregular heartbeat

• Swelling in the neck

Interestingly, tiredness can occur with both conditions, which is one reason symptoms alone cannot confirm whether you have a thyroid disorder. A proper assessment and blood test are needed.

Underactive thyroid symptoms

Symptoms of an underactive thyroid often develop gradually.

Because they can be mild or easily confused with stress, a busy lifestyle, ageing, menopause or other health concerns, some people live with them for a long time before seeking medical advice.

Are you tired all the time?

Thyroid hormones influence the way your body uses energy. When levels are low, you may feel unusually tired, sluggish or physically drained.

This can feel different from simply needing an early night. You might sleep for several hours and still wake up feeling as though you haven't properly rested.

Everyday tasks may begin to require much more effort than they used to.

Do you feel cold when everyone else is warm?

Feeling cold more than usual is a recognised symptom of an underactive thyroid.

You may notice that your feet are especially cold, or that you need extra layers when everyone else seems perfectly comfortable.

For me, this was incredibly relatable. I could be lying in bed during warm weather while everyone else felt hot, yet my body still felt so cold that I needed to put on socks.

It can seem like a small or even slightly unusual habit, so you may not recognise it as something worth mentioning to your GP. However, when it appears alongside other symptoms, it can be an important clue.

Is your hair shedding or becoming thinner?

An underactive thyroid can be associated with dry hair, thinning hair or hair loss.

This was one of the symptoms that finally pushed me to seek help.

My hair was shedding so much that I remember crying and making a doctor's appointment because I genuinely thought I was becoming bald. It wasn't about vanity; it was frightening to see such a visible change without understanding why it was happening.

Hair loss can have many different causes, including iron deficiency, stress and hormonal changes, so it is important not to assume that the thyroid is always responsible. Speak to your GP if the shedding is persistent or significant.

Are you struggling to concentrate?

Difficulty concentrating or thinking clearly is sometimes described as “brain fog”.

You may find it harder to:

• Remember information

• Find the right words

• Focus on a conversation

• Complete tasks

• Organise your thoughts

When you are managing work, children, a home and countless everyday responsibilities, brain fog can feel particularly frustrating.

Are you gaining weight or finding weight management harder?

An underactive thyroid can slow the body's metabolic processes and may contribute to weight gain.

However, thyroid-related weight gain is often more complex than simply gaining body fat. Changes in salt and water balance can also play a role, and significant weight changes should always be discussed with a healthcare professional.

Once thyroid levels are properly managed, sustainable habits such as balanced nutrition, movement, sleep and stress management remain important.

Having an underactive thyroid does not mean that your health goals are impossible. It may simply mean that your body needs appropriate medical treatment, realistic expectations and a more patient approach.

Have your digestion or bowel habits changed?

Constipation is another common symptom of hypothyroidism because the digestive system may slow down.

Some people may also experience:

• Sluggish digestion

• Abdominal discomfort

• A feeling of heaviness

• Changes in regularity

These symptoms can have many causes, so speak to your GP if they are persistent, painful or significantly different from what is normal for you.

Have your periods become heavier or irregular?

An underactive thyroid can affect menstrual cycles.

Some women experience heavier, longer or irregular periods. Because period changes can also be connected to conditions such as perimenopause, fibroids, polycystic ovary syndrome or endometriosis, they should be properly assessed rather than automatically attributed to the thyroid.

What causes an underactive thyroid?

There is no single cause of hypothyroidism.

An autoimmune condition

In the UK, a common cause is an autoimmune condition called Hashimoto's thyroiditis.

This happens when the immune system mistakenly attacks the thyroid gland, gradually affecting its ability to produce enough thyroid hormone.

Previous thyroid treatment

An underactive thyroid can develop following:

• Thyroid surgery

• Radioactive iodine treatment

• Certain treatments for an overactive thyroid

Certain medicines

Some medicines can affect thyroid function.

Never stop taking prescribed medication without speaking to your doctor. Your GP or pharmacist can advise you if a medicine may be affecting your thyroid.

Problems with the pituitary gland

In less common cases, hypothyroidism may be connected to the pituitary gland, which helps regulate thyroid hormone production.

Thyroid problems from birth

A small number of babies are born with an underactive thyroid. Newborn screening helps identify congenital hypothyroidism early.

Can an underactive thyroid be prevented?

In many cases, an underactive thyroid cannot be prevented.

For example, you cannot reliably prevent an autoimmune condition such as Hashimoto's, and there is no guaranteed food, supplement or lifestyle habit that will stop hypothyroidism from developing.

What you can do is:

• Pay attention to persistent symptoms

• Speak to your GP when something feels wrong

• Attend recommended blood tests

• Take prescribed medication consistently

• Avoid unregulated products claiming to “boost” or “cure” the thyroid

• Follow a balanced lifestyle that supports your overall health

Early recognition and appropriate treatment can make the condition much easier to manage.

How is an underactive thyroid diagnosed?

Hypothyroidism is usually diagnosed through a blood test.

Your GP will commonly assess:

• TSH, or thyroid-stimulating hormone

• Free T4, one of the main thyroid hormones

Depending on your symptoms and results, further tests may sometimes be recommended.

Symptoms alone cannot diagnose a thyroid condition because tiredness, hair loss, weight changes and brain fog can also occur with iron deficiency, vitamin deficiencies, stress, menopause and several other conditions.

If you recognise yourself in this article, use it as a reason to speak to your GP rather than trying to diagnose yourself.

Is there a cure for an underactive thyroid?

This is one of the most frequently searched questions about hypothyroidism.

For most people, the condition is managed rather than cured.

The standard treatment is usually a daily medicine called levothyroxine. This replaces the thyroxine hormone that the thyroid is not producing in sufficient amounts.

Many people need treatment for life, although individual circumstances vary. Your dose may be adjusted according to your symptoms and blood test results.

Never change your dose or stop taking thyroid medication without medical advice.

How should levothyroxine be taken?

Follow the instructions given by your GP, pharmacist and the information supplied with your medication.

NHS guidance generally advises taking levothyroxine once a day, ideally at least 30 minutes before breakfast or a drink containing caffeine. It should normally be swallowed with water.

Some foods, supplements and medicines can affect how well levothyroxine is absorbed. Calcium-rich foods, calcium supplements, iron supplements, antacids and some other medicines may need to be separated from your thyroid medication.

Because the correct timing can depend on the product and your wider medication routine, ask your pharmacist for personalised advice rather than guessing.

What foods should you eat with an underactive thyroid?

There is no special diet that cures hypothyroidism.

A balanced, varied diet is generally more beneficial than following a highly restrictive “thyroid diet”.

Aim to include a mixture of:

• Vegetables and fruit

• Protein-rich foods

• Beans and lentils

• Eggs

• Fish

• Wholegrains

• Nuts and seeds

• Healthy fats

• Fibre-rich foods

Eating balanced meals can help support energy, digestion, muscle health and overall wellbeing, but food should complement appropriate medical care rather than replace it.

What foods should you avoid with an underactive thyroid?

This is another area where there is a lot of confusing information online.

Most people with hypothyroidism do not need to completely remove everyday foods such as broccoli, kale, cabbage, cauliflower or soya from their diet.

For most people, these foods can still form part of a varied, balanced diet.

The more important considerations are usually medication timing and avoiding unnecessary high-dose supplements.

Be cautious with iodine and kelp supplements

Iodine is needed for thyroid hormone production, but more is not always better.

Products containing large amounts of iodine, kelp or sea moss are sometimes marketed as thyroid boosters. However, excessive iodine may interfere with thyroid function, and these products are not a substitute for prescribed treatment.

The British Thyroid Foundation advises people with a diagnosed thyroid condition to avoid kelp and sea moss products marketed as thyroid supplements.

Consider the timing of calcium and iron

Calcium and iron can interfere with the absorption of levothyroxine.

This does not mean you must avoid calcium- or iron-containing foods entirely. It means you may need to leave an appropriate gap between your medication and certain foods or supplements.

Ask your pharmacist how to organise your personal routine safely.

Be consistent with soya

Soya foods can usually still be enjoyed, but they may affect the absorption of levothyroxine in some circumstances.

If soya is a regular part of your diet, consistency is helpful, and your healthcare professional may consider this when reviewing your thyroid levels or medication dose.

Can lifestyle changes help?

Lifestyle changes cannot replace thyroid medication when it is medically required, but they can support your wider health and help you manage some of the challenges associated with hypothyroidism.

Take your medication consistently

Taking your medicine as prescribed and attending follow-up blood tests are two of the most important parts of thyroid management.

Build balanced meals

Try to include protein, fibre, carbohydrates and healthy fats rather than relying on overly restrictive diets.

Eating too little or continually moving between extreme diets can leave you feeling even more tired and make healthy routines harder to maintain.

Move your body regularly

Walking, strength training, swimming, stretching and other enjoyable forms of movement can support physical and emotional wellbeing.

Begin at a realistic level, particularly if fatigue or muscle aches are affecting you. Consistency is more valuable than punishing yourself with a routine you cannot sustain.

Protect your sleep

Poor sleep can make tiredness, cravings, concentration and mood feel more difficult.

A regular bedtime, reduced screen use before sleeping and a calm evening routine may help support better rest.

Manage stress where possible

Stress does not automatically cause hypothyroidism, but ongoing stress can make daily symptoms feel harder to manage.

Even small moments of rest can be valuable:

• A short walk

• A warm shower

• Quiet prayer or reflection

• A few minutes away from your phone

• Preparing a warm drink

• Asking for help when you need it

Where KAWA fits into my routine

KAWA is not a treatment or cure for an underactive or overactive thyroid. It should not replace levothyroxine, blood tests, medical advice or any treatment recommended by your healthcare professional.

For me, KAWA is part of a wider self-care routine.

It gives me a simple daily ritual that reminds me to pause, stay connected to my wellbeing and make a little space for myself.

Because herbal products may interact with medicines or may not be appropriate for everyone, speak to your GP or pharmacist before introducing any herbal product if you take regular medication or have a diagnosed health condition.

When taking levothyroxine, follow the instructions for taking it with water and leaving the recommended time before consuming food or other drinks.

When should you speak to your GP?

Consider arranging a GP appointment if you are experiencing persistent symptoms such as:

• Ongoing tiredness

• Feeling unusually cold

• Significant hair shedding

• Unexplained weight changes

• Constipation

• Difficulty concentrating

• Dry skin or hair

• Low mood

• Heavy or irregular periods

• Swelling at the front of your neck

Seek urgent medical advice if you experience severe symptoms such as chest pain, fainting or a very fast or irregular heartbeat.

A blood test may help establish whether your thyroid is contributing to your symptoms or whether another cause needs to be investigated.

A final thought from me

Being diagnosed with an underactive thyroid gave me something I desperately needed: an explanation.

It helped me understand that I wasn't simply lazy, weak or failing to try hard enough. My body was asking for the right support.

Living with hypothyroidism has taught me to pay attention to my body, remain consistent with my treatment and be more patient with myself.

You deserve that same patience too.

You do not need to diagnose yourself through social media, purchase every supplement marketed as a solution or blame yourself for symptoms you don't yet understand.

Start by listening to your body and asking for professional help.

Sometimes, understanding what is happening is the first and most important act of self-care.

Frequently asked questions

What are the first signs of an underactive thyroid?

Early symptoms can include persistent tiredness, feeling cold, constipation, dry skin, hair thinning, low mood, difficulty concentrating and weight gain. Symptoms often develop gradually and can be easy to overlook.

Can an underactive thyroid be cured naturally?

There is no food, herbal remedy or lifestyle practice proven to cure hypothyroidism. Most people manage it with prescribed thyroid hormone replacement and regular monitoring.

Can you lose weight with an underactive thyroid?

Yes, having an underactive thyroid does not make weight management impossible. Appropriate thyroid treatment, balanced nutrition, regular movement, sleep and realistic expectations can all support your wider health.

Which foods should you avoid with hypothyroidism?

Most people do not need to avoid entire food groups. The main considerations are taking levothyroxine correctly, separating it from certain supplements or foods when advised, and avoiding high-dose iodine, kelp or sea moss products marketed as thyroid boosters.

Do broccoli and cabbage make hypothyroidism worse?

Most people can eat cruciferous vegetables such as broccoli, cabbage, kale and cauliflower in normal portions as part of a varied diet. You do not usually need to remove nutritious vegetables unless a qualified healthcare professional has advised you to do so.

Is an underactive thyroid more common in women?

Yes, hypothyroidism is more common among women. Anyone can develop it, however, so persistent symptoms should be assessed regardless of sex or age.

How is an underactive thyroid treated?

The standard treatment is usually daily levothyroxine, which replaces the thyroid hormone the body is not producing adequately. Blood tests are used to monitor thyroid levels and guide the dose.

Can an underactive thyroid cause hair loss?

Dry hair, thinning hair and hair loss can occur with hypothyroidism. However, hair loss can also have other causes, so significant or persistent shedding should be discussed with your GP.

This article is for general educational purposes and does not provide individual medical advice. It should not be used to diagnose or treat a thyroid condition. Speak to your GP, pharmacist or another qualified healthcare professional if you have symptoms, take regular medication or need advice about your personal circumstances.