Lithium and High TSH: Does Lithium Cause an Underactive Thyroid?

Yes. Lithium can cause an underactive thyroid (hypothyroidism), and a raised TSH is often the first sign on a blood test. A large UK study summarised by the American Thyroid Association found lithium use was linked to a higher risk of hypothyroidism, mostly early in treatment, in people with higher lithium levels and most often in women under 60.

A high TSH on lithium does not mean lithium is the only possible cause, and it is not a reason to stop the medicine on your own. The prescriber looks at your free T4, symptoms, earlier results and mental health together before deciding what, if anything, needs to change.

This guide is for adults taking lithium who want to understand a thyroid result. Our separate guide on high TSH with normal free T4 explains that result pattern in general.

The NHS describes lithium toxicity as an emergency. If you have signs of it, the NHS advises stopping lithium and getting urgent medical help: call emergency services or go to an emergency department now, and tell staff you take lithium. Signs include:

Outside of these emergency signs, do not stop or change lithium on your own; the NHS advises against stopping it suddenly, so talk to your prescriber first.

• Confusion, blackouts or difficulty speaking.
• Feeling very thirsty and passing much more urine than usual.
• Losing control of your bladder or bowels.
• Severe vomiting or diarrhoea, marked drowsiness, unsteadiness, blurred vision or muscle weakness, which MedlinePlus lists among signs of too much lithium.
• Very slow heartbeat, extreme lethargy, trouble breathing or a low body temperature, which Cleveland Clinic lists as possible signs of a severe underactive thyroid.

The NHS lists tiredness, weight gain and feeling depressed as common signs of an underactive thyroid in people taking lithium. Other symptoms of an underactive thyroid include feeling cold, constipation, dry skin or hair loss, poor concentration and changes in periods.

Some of these overlap with low mood or with lithium's other effects, so they are easy to miss or misread. That is one reason routine blood tests matter even when you feel well. If you notice new or worsening symptoms, tell your care team rather than waiting for the next scheduled test.

The NHS and the NHS Specialist Pharmacy Service set out routine monitoring. Local plans differ, but the usual pattern is:

• Before starting: thyroid function tests, kidney function (eGFR, urea and electrolytes), blood calcium, a full blood count and weight or BMI. The Specialist Pharmacy Service says people should have normal thyroid function before lithium is started.
• Lithium blood levels: weekly at first until stable, then regularly. The NHS says once stable, levels are usually checked every 3 to 6 months, with the sample taken 12 hours after the last dose.
• Ongoing: thyroid function, kidney function, calcium and weight every 3 to 6 months, according to the Specialist Pharmacy Service.
• More often: for example, in people aged 65 or over, those taking medicines that interact with lithium, those at risk of thyroid or kidney problems, those with raised calcium, or during pregnancy.

In the UK laboratory study summarised by the American Thyroid Association, most thyroid problems appeared early in treatment and were more common in people with higher blood lithium levels. Women under 60 were affected most often. The same study did not find a higher risk of an overactive thyroid.

That does not mean later changes cannot happen. Thyroid tests continue for as long as lithium is taken, because the kidneys, thyroid and calcium balance can all change over time. Keeping your results in one place, such as a lithium booklet or record, makes it easier for any clinician to spot a trend rather than react to one number.

The NHS notes that taking lithium for a long time can cause problems with the kidneys as well as the thyroid. Kidney function also affects how lithium is cleared from the body, so the NHS says people with kidney problems need their lithium level watched more closely.

The American Thyroid Association notes that lithium has been linked with parathyroid problems. The parathyroid glands control calcium, which is why blood calcium is part of routine monitoring. If your calcium is raised, our guide on a high calcium blood test explains what clinicians usually look at next, such as PTH.

No, not on your own. Do not stop lithium or change your dose without talking to the prescriber. The NHS says symptoms are likely to return if lithium is stopped suddenly, and if stopping is ever agreed, the dose is reduced gradually over weeks or months.

A raised TSH is a finding to discuss, not a reason to stop. Depending on the full results, the clinician may repeat the test, check thyroid antibodies, start thyroid treatment or involve an endocrinologist. Decisions about lithium itself are usually made with the mental health team, weighing how well it is working for you.

Clinicians still consider other causes of a raised TSH, such as autoimmune thyroid disease, other medicines, recent illness and the timing of the test. Reference ranges differ between laboratories, so check the range on your own report.

Bring your lithium booklet or record, recent and earlier thyroid, kidney and calcium results with dates, and a list of all medicines and supplements.

• Is my raised TSH likely related to lithium, or are other causes possible?
• What is my free T4, and do I need a repeat test or a thyroid antibody test?
• Would thyroid treatment be considered, and how would it be monitored?
• Are my kidney function and calcium results stable compared with before?
• Should my tests be more frequent for now, and who will contact me with results?
• Which symptoms mean I should call before my next blood test?

On SameCase, patients and verified doctors share de-identified cases. Reading how others taking lithium described a raised TSH, their monitoring schedule and the questions they asked can help you prepare for your own appointment.

Other people's cases cannot tell you what your result means or whether your treatment should change. Use them to shape your questions, then talk with the prescriber who knows your full history.