Hypothyroidism: symptoms, blood tests and treatment
An underactive thyroid develops slowly, and the symptoms are the sort that get attributed to a busy life: tiredness, weight gain, feeling cold, low mood. It is diagnosed on a blood test and treated with a single daily tablet, but the details of that tablet, and of the monitoring around it, decide whether treatment works. This page covers symptoms, testing, treatment, monitoring and the situations that need urgent attention.
What are the symptoms of an underactive thyroid?
The thyroid sets the pace of the body's metabolism, so when it slows, everything slows with it. The commonest symptoms are persistent tiredness, weight gain despite unchanged eating, feeling cold when others are comfortable, constipation, dry skin, brittle hair and hair thinning, and a low, flat mood with slowed thinking.
Other features include muscle aches and cramps, hoarseness, puffiness around the eyes and face, heavier or irregular periods, reduced fertility, a slow pulse and raised cholesterol found incidentally on a blood test. Some people notice a swelling in the front of the neck.
No single symptom means very much on its own, and that is the difficulty: each of these has many other explanations, and they build up gradually enough that people adapt without noticing. Because the picture is non-specific, hypothyroidism is diagnosed on blood tests rather than on symptoms, and symptoms alone are never a reason to start or change treatment.
What causes it?
In Ireland and across Europe the commonest cause is autoimmune thyroiditis, often called Hashimoto's disease, in which the immune system gradually damages the thyroid gland. It is more common in women and becomes more common with age, and it often runs alongside other autoimmune conditions such as coeliac disease or type 1 diabetes.
The other frequent causes are treatments to the thyroid itself: surgical removal of part or all of the gland, radioactive iodine treatment for an overactive thyroid, or radiotherapy to the neck. Certain medicines interfere with thyroid function, including amiodarone, lithium and some cancer treatments, which is why thyroid tests are monitored for people taking them.
Less commonly, the problem lies in the pituitary gland rather than the thyroid, and rarely a baby is born with an underactive thyroid, which is why newborn screening exists. Iodine deficiency is a major cause worldwide but is uncommon here. Pregnancy and the months after delivery can also unmask or cause thyroid problems.
Which blood tests are used?
The first test is thyroid stimulating hormone, TSH, the signal the pituitary sends to the thyroid. When the thyroid is underactive, the pituitary pushes harder and TSH rises. Free thyroxine, free T4, is measured alongside it to see what the gland is actually producing.
A raised TSH with a low free T4 indicates primary hypothyroidism and is normally treated. A raised TSH with a free T4 still inside the reference range is called subclinical hypothyroidism, and whether to treat it depends on how high the TSH is, on symptoms, on antibodies, on age and on pregnancy plans; sometimes the right answer is to repeat the test rather than to start a tablet.
Thyroid peroxidase antibodies can be measured to identify autoimmune disease and to estimate the likelihood of progression. An abnormal result is usually confirmed on a repeat sample before treatment begins, because temporary changes occur during and after other illnesses. Reference ranges differ between laboratories, so results should be interpreted against the range printed on your own report.
How is it treated?
Treatment is levothyroxine, a synthetic form of the hormone the thyroid should be making. It is taken once daily, and for most people it is lifelong. The starting dose depends on age, weight, how underactive the gland is and whether there is heart disease; in older people and in those with angina, treatment is started low and increased gradually.
How you take it matters as much as the dose. Levothyroxine is absorbed best on an empty stomach, typically taken with water and separated from food. Calcium and iron supplements, indigestion remedies containing antacids, and some other medicines interfere with absorption and should be separated by several hours. Keep to the same routine every day so that blood tests reflect a consistent pattern.
Levothyroxine is a prescription-only medicine, and different products are not always interchangeable, so it is worth staying on the same preparation where possible. Combination treatment with liothyronine is used only in specific circumstances under specialist supervision, and it is not a routine option.
How is treatment monitored?
After starting levothyroxine, or after any dose change, thyroid function is rechecked after about six to eight weeks, because the level takes that long to settle at the new dose. Testing sooner gives a misleading picture and leads to unnecessary changes.
Once the dose is stable and you feel well, testing is usually repeated annually, and sooner if symptoms change, if you become pregnant, if you start a medicine that affects absorption, or if your weight changes substantially. This ongoing monitoring is the reason a repeat prescription is assessed against recent results rather than issued indefinitely.
Too much levothyroxine is not harmless. Over-treatment produces palpitations, tremor, anxiety, insomnia, heat intolerance and weight loss, and over years it raises the risk of atrial fibrillation and of thinning of the bones. That is why doses are not increased on the basis of tiredness alone, and why using levothyroxine for weight loss in someone with a normal thyroid is both ineffective and unsafe.
When do I need medical help without delay?
Call 112 or 999 if someone with an underactive thyroid becomes very drowsy or unrousable, confused, unusually cold to the touch, or is breathing slowly and shallowly, particularly an older person during cold weather or an untreated or undertreated patient after an infection or a fall. Severe untreated hypothyroidism can progress to a life-threatening state and is a medical emergency.
Seek urgent medical advice for chest pain, breathlessness, a pounding or irregular heartbeat, or fainting, particularly after starting levothyroxine or increasing the dose. In people with heart disease, dose increases are made cautiously for exactly this reason.
Arrange an assessment promptly if you are pregnant or planning pregnancy while on levothyroxine, because requirements usually rise early and the dose needs reviewing without waiting for a routine test. Do the same for a rapidly enlarging neck swelling, difficulty swallowing or breathing, a hoarse voice lasting more than a few weeks, or severe low mood and thoughts of self-harm. If you are in distress and need to talk, Samaritans can be reached free on 116 123.
Living with an underactive thyroid
Treated adequately, hypothyroidism does not shorten life or limit what you can do, and most symptoms resolve over weeks to months. Improvement is gradual rather than immediate, and hair and skin are usually the slowest to recover, which is worth knowing so the treatment is not abandoned too early.
Do not stop or adjust the dose yourself because you feel better; the underlying condition has not gone away, and levels drift back within weeks. Keep a note of your dose and the brand you take, carry it when you travel, and mention it whenever another medicine is started, because interactions with absorption are common and easily managed once known.
Iodine supplements and kelp preparations are widely sold for thyroid health. They are not helpful in autoimmune hypothyroidism and excess iodine can make thyroid function worse, so they are best avoided unless a doctor advises otherwise. If tiredness persists despite normal blood results, the answer is usually to look for another cause, such as anaemia, coeliac disease, sleep problems or depression, rather than to raise the dose.
Is levothyroxine treatment for life?
Usually yes, because the underlying damage to the gland does not reverse. Exceptions exist: thyroid inflammation after a viral illness or after pregnancy can be temporary, and in those cases a doctor may plan a trial of stopping with blood tests afterwards. That decision belongs to the doctor monitoring you.
Why do I still feel tired although my blood tests are normal?
Persistent tiredness with normal thyroid results usually has another explanation, such as anaemia, vitamin B12 or iron deficiency, coeliac disease, sleep apnoea, depression or another chronic condition. Raising the levothyroxine dose in that situation risks over-treatment without solving the problem.
Can I take my levothyroxine with breakfast?
Absorption is best on an empty stomach with water, separated from food, and away from coffee, calcium, iron and antacids. Some people take it at night instead, several hours after the last meal. Consistency matters more than the exact hour, since blood tests are interpreted against your usual routine.
Does an underactive thyroid cause weight gain?
It causes some weight gain, largely fluid retention and a modest fall in metabolic rate, and treatment reverses part of it. It does not explain large weight gain, and levothyroxine is not a weight-loss treatment. Taking it without a thyroid deficiency causes harm without benefit.
What happens to my dose in pregnancy?
Thyroid hormone requirements usually increase early in pregnancy, and untreated or undertreated hypothyroidism matters for the pregnancy, so the dose is reviewed as soon as pregnancy is confirmed and monitored more frequently. Contact the doctor who manages your treatment without waiting for a routine appointment.