Underactive Thyroid
A thyroid that’s running slow, so everything else runs slow too: tiredness, feeling cold, constipation, low mood. Diagnosed with a simple blood test and treated with one small tablet a day, usually for life.
Typical signs: tiredness, feeling cold, weight gain, constipation, poor concentration, low mood, dry skin and hair, a hoarse voice, and irregular or heavy periods. Often mild and slow to build.
Why it happens: most often Hashimoto’s disease, where the immune system attacks the thyroid. It’s most common in women and often starts between 30 and 50. Other causes are thyroid surgery, radioactive iodine or radiotherapy, some medicines and, rarely, low iodine.
Diagnosis: blood tests for TSH and T4. A high TSH means the brain is shouting at a sluggish thyroid. A mildly high TSH with normal T4 is called subclinical, and often doesn’t need treatment.
The thyroid ladder
One tablet, taken properly, fixes most of this. The fiddly part is finding the right dose, which takes a few blood tests.
- Step 1 · PrescriptionLevothyroxineA daily tablet that replaces the missing hormone. Older people and those with heart disease start low.
- Works
- Replaces what’s missing; most people live a normal life on it
- Cost
- Under the $25 PBS co-payment; $7.70 concession
- How long
- Usually for life
- Watch for
- Too high a dose: palpitations, poor sleep, anxiety, sweating, diarrhoea or headaches.
Small tablet, big job, zero tolerance for being taken with breakfast.
- Step 2 · Self-careTake it the right wayOn an empty stomach with water, 30–60 minutes before food, coffee or tea, at the same time each day. Keep iron and calcium supplements well apart.
- Works
- Food, coffee, iron and calcium cut absorption and can make the dose look wrong
- Cost
- Free
- How long
- Every day
- Watch for
- Biotin supplements can scramble thyroid blood tests; tell your GP if you take them.
The coffee can wait half an hour. It will still be there.
- Step 3 · Self-careBlood tests on scheduleTSH every 3 months until the dose is stable, then once a year. More often in pregnancy.
- Works
- TSH can take up to 6 months to settle after starting
- Cost
- Usually covered by Medicare
- How long
- Ongoing
- Watch for
- Bring a list of other medicines; several interact.
The blood test steers. Your mood on a Tuesday doesn’t.
- Step 4 · PrescriptionBorderline (subclinical) resultsMildly raised TSH with normal T4.
- Works
- Guidelines suggest treatment if TSH is 10 or more on two tests 3 months apart; under 65 with symptoms, a 6-month trial, stopped if no better
- Cost
- Under the $25 PBS co-payment if treated
- How long
- Repeat tests to confirm
- Watch for
- One high result during an illness isn’t a diagnosis; repeat it.
A number slightly out of range is a reason to recheck, not panic.
- Step 5 · SpecialistEndocrinologistFor pregnancy with thyroid disease, unusual results, children, or symptoms that persist despite normal tests.
- Works
- Needed by a minority
- Cost
- Specialist fees vary; Medicare rebates with a GP referral
- How long
- Varies
- Watch for
- Most people are managed well by their GP.
The thyroid’s fan club, for the tricky cases.
Save your money
Popular, heavily marketed or often asked about, but the evidence is weak or says no.
- Adding T3 (liothyronine)Guidelines don’t routinely recommend it: benefits over levothyroxine alone aren’t established and long-term effects are uncertain.
- “Natural” or desiccated thyroid extractNot recommended: inconsistent and of uncertain safety. Natural isn’t the same as reliable.
- Treating every slightly high TSHMany borderline results don’t need treatment, especially without symptoms. Recheck first.
What you can do
- Take your tablet at the same time each day, on an empty stomach.
- Keep iron, calcium and antacids a few hours away from your dose.
- Tell your GP early if you’re pregnant or planning a pregnancy.
- Mention biotin or “hair and nail” supplements before blood tests.
- Report palpitations, shakiness or poor sleep: the dose may be too high.
See your GP if
- You have several of the symptoms above
- You’re on levothyroxine and still feel unwell, or feel jittery
- You’re pregnant or planning to be
- You have type 1 diabetes or another autoimmune condition and haven’t been tested
- You notice a lump or swelling in your neck
Pregnant or planning? Tell your GP early: the dose often needs to rise, and untreated hypothyroidism raises the risk of miscarriage, pre-eclampsia and premature birth. Get emergency help (call 000 (Australia) or your local emergency number. From a mobile, 112 works in most countries.) for a high temperature with a fast or irregular heartbeat on levothyroxine, or severe drowsiness and confusion in someone with untreated hypothyroidism.
Common questions
Is levothyroxine for life?
Usually, yes. Most people with an underactive thyroid take it for life and live a normal life. The dose may change over time, so regular blood tests are needed.
Can I take levothyroxine with coffee?
Take it with water on an empty stomach, 30 to 60 minutes before food, coffee or tea. Coffee and food reduce how much you absorb.
How long until the dose is right?
TSH is checked every 3 months until it is stable, then once a year. After a very high starting TSH it can take up to 6 months to settle.
Should I take T3 or natural thyroid extract?
Guidelines do not routinely recommend T3 or natural thyroid extract, because they have not been shown to work better than levothyroxine and their long-term safety is uncertain.
Helpful resources
- NHS: LevothyroxineHow to take it, interactions and side effects in plain English. Free, UK.
- NHS: Underactive thyroidSymptoms, causes and pregnancy advice. Free, UK.
Evidence and more information
- NHS: Underactive thyroid (hypothyroidism)
- NHS: Levothyroxine
- NICE NG145: Thyroid disease, assessment and management
maladywise.com/underactive-thyroid/