Lithium and Thyroid Disease: How It Affects Your Thyroid and What to Do About It

When you’re taking lithium for bipolar disorder, the goal is simple: keep your moods stable. But for many people, that stability comes with an unexpected cost-your thyroid. Lithium doesn’t just affect your brain. It quietly interferes with how your thyroid works, often without warning. By the time you feel the fatigue, weight gain, or cold intolerance, your thyroid function may already be significantly off. This isn’t rare. About one in five people on long-term lithium develop hypothyroidism. For some, it’s worse. Up to half develop a goiter. And while most cases are manageable, many patients and doctors still don’t know how to handle them properly.

How Lithium Breaks Down Thyroid Function

Lithium doesn’t attack your thyroid like a virus. It sneaks in and disrupts the machinery. Your thyroid makes hormones-T4 and T3-that control your metabolism, energy, temperature, and mood. Lithium messes with every step of that process. It blocks iodine from attaching to thyroglobulin, the protein that holds the building blocks of thyroid hormone. It stops the thyroid from releasing the hormones it already made. It even reduces how much T4 gets turned into the more active T3 in your body.

On top of that, lithium causes thyroid cells to swell and multiply. That’s why so many people on lithium develop goiters-enlarged thyroids. Studies show 30% to 59% of long-term users get one. In places like Denmark, where iodine intake is moderate, that number climbs to 50% after ten years. In the U.S., it’s closer to 30%, thanks to iodized salt. But even then, it’s still common.

What’s worse, lithium doesn’t just cause low thyroid function. It can also trigger hyperthyroidism in 3% to 5% of users. This isn’t Graves’ disease, the classic autoimmune form. It’s usually painless thyroiditis-where the thyroid leaks hormones briefly, then settles down. It often resolves on its own in a few months. But it’s easy to mistake for something more serious. And if you’re not monitored, you could end up with the wrong treatment.

Who’s Most at Risk?

Not everyone on lithium gets thyroid problems. But some people are far more likely to. Women under 60 are at the highest risk-three times more likely than men to develop hypothyroidism on the same dose. Age matters too. The longer you take lithium, the higher your risk. After five years, nearly half of patients show signs of thyroid trouble. After ten years, it’s nearly universal.

Other factors pile on. If you already have thyroid antibodies, even before starting lithium, your chances of developing dysfunction jump. Women with a family history of autoimmune thyroid disease are especially vulnerable. And if you’re on other medications-like antidepressants or gabapentin-that can also affect your thyroid, your risk goes up even more.

One surprising finding from a 2024 study: lithium dose matters. For every extra 100 mg per day, your odds of thyroid problems increase by 27%. That means someone on 900 mg daily has a much higher risk than someone on 600 mg. But here’s the twist: the longer you’re on lithium, the more your thyroid seems to adapt. The risk doesn’t keep climbing forever. It plateaus. That’s why some people on lithium for 15 years have normal thyroid levels, while others develop problems after just two.

Monitoring: What You Need to Do

There’s no way around it: if you’re on lithium, you need regular thyroid tests. Not every six months. Not just when you feel bad. Always. The American Thyroid Association says baseline testing before you start is non-negotiable. Then, check TSH and free T4 every six months for the first year. After that, once a year is fine-if your levels are stable.

But here’s where things go wrong. Many primary care doctors panic when they see a slightly high TSH in the first few months. They assume it’s permanent. They push for lithium to be stopped. But it takes six to eight weeks for lithium to fully affect thyroid function. A TSH of 5.5 at three months doesn’t mean you need to quit. It might just be the beginning. Stopping lithium too early can mean losing the only medication that truly prevents suicide in bipolar disorder.

A 2022 study found that 23% of patients had their lithium stopped unnecessarily because of early TSH spikes. That’s dangerous. You don’t treat a mild TSH rise with medication unless it’s over 10 and you have symptoms. Watch. Wait. Re-test. Don’t rush.

Managing Hypothyroidism on Lithium

If your thyroid slows down, levothyroxine is the fix. But it’s not as simple as taking a pill and calling it done. People on lithium often need 20% to 30% more levothyroxine than someone with the same TSH level who isn’t on lithium. Why? Lithium interferes with how your body uses the hormone. So even if your TSH looks normal, you might still feel tired, cold, or gain weight.

Start low-25 to 50 mcg per day. Re-test TSH in six weeks. Adjust slowly. Don’t chase a TSH of 1.0. Aim for 2.0 to 4.0. That’s the sweet spot for most people on lithium. And keep checking every six months. Your dose might need to change over time, even if your lithium dose hasn’t.

Some patients report feeling off even with perfect TSH numbers. That’s real. It might be low T3, or your body’s sensitivity to hormones has changed. Don’t dismiss it. Talk to your doctor about testing free T3. If you’re still symptomatic, ask about adding a small dose of T3 (liothyronine). It’s not standard, but it helps some people.

Handling Hyperthyroidism

Hyperthyroidism on lithium is rare, but it happens. Most cases are painless thyroiditis. You might feel shaky, sweaty, or have a fast heartbeat. But no pain. No eye changes. No weight loss. That’s a clue. If you have those symptoms and a high T3/T4 with a low TSH, your doctor needs to rule out Graves’ disease.

Graves’ disease is rare with lithium-less than 1% of cases. But if it’s confirmed, you’ll need antithyroid drugs like carbimazole. Start at 20 mg daily. You might also need steroids if inflammation is high.

But for painless thyroiditis? Do nothing. Let it run its course. It usually resolves in three to six months. Don’t give beta-blockers unless your heart rate is dangerously high. Don’t use radioactive iodine or surgery. You’re not treating an autoimmune disease. You’re waiting out a temporary leak.

The Big Trade-Off: Lithium vs. Alternatives

It’s tempting to switch to another mood stabilizer because of thyroid issues. Valproate? It can cause mild TSH spikes in 5-10% of users. Carbamazepine? Almost no thyroid effect. But here’s the catch: none of them are as good as lithium at preventing suicide.

A 2017 meta-analysis showed lithium reduces the risk of any mood episode by 39% compared to placebo. A 2013 BMJ study found it cuts suicide attempts by 14% more than other drugs. That’s huge. For many, lithium is the only thing keeping them alive.

So switching isn’t always the answer. It’s about managing the thyroid problem while keeping the mood stability. That’s why most psychiatrists keep patients on lithium-even with hypothyroidism-and just add levothyroxine. It’s not ideal, but it’s the best balance.

New Hope: What’s Changing

There’s new research offering better ways to handle this. A 2023 trial showed that taking 100 mcg of selenium daily cut the rate of hypothyroidism in lithium users from 24% to 14% over two years. Selenium helps your thyroid process iodine and reduces inflammation. It’s safe, cheap, and easy. Ask your doctor if it’s right for you.

Another promising development: a predictive algorithm from 2024. It uses your age, gender, baseline TSH, and other meds to estimate your risk of thyroid decline. If your score is high, you can start selenium early, check your thyroid more often, or adjust your lithium dose before problems hit.

And in the future, we might not even need lithium as we know it. A new compound, RG101, is in Phase II trials. It works like lithium for mood but doesn’t mess with the thyroid. Early results show normal TSH levels in patients. If it works, it could replace lithium for many.

What Patients Are Saying

On Reddit, people on lithium share real stories. One wrote: ‘My TSH went from 1.8 to 8.7 in 18 months. I take 75 mcg levothyroxine now. But my psychiatrist won’t lower my lithium dose-even though I’m tired all the time.’ Another said: ‘On 900 mg for eight years. My thyroid is perfect. Every test normal.’

The divide is real. Some struggle. Others don’t. But almost everyone who has issues says the same thing: ‘I’d rather have this fatigue than another manic episode.’ That’s the truth. Lithium isn’t perfect. But for many, it’s the price of survival.

Final Takeaways

• Lithium causes thyroid problems in up to 32% of long-term users-mostly hypothyroidism.
• Women, older patients, and those on higher doses are at greatest risk.
• Check TSH and free T4 before starting lithium, then every 6 months for the first year, then yearly.
• Don’t stop lithium for a mildly elevated TSH in the first 3 months. Wait and re-test.
• Levothyroxine is the standard treatment for hypothyroidism-but you may need a higher dose than usual.
• Painless thyroiditis (hyperthyroidism) usually goes away on its own. Don’t over-treat it.
• Selenium (100 mcg/day) may reduce your risk of thyroid damage.
• Lithium’s suicide prevention benefits outweigh thyroid risks for most people.

What to Do Next

If you’re on lithium and haven’t had a thyroid test in over a year, schedule one now. If you’re newly diagnosed and starting lithium, ask your doctor about baseline testing and selenium. If you’re already on levothyroxine and still feel tired, ask about checking free T3. Don’t assume your thyroid is fine because your TSH is ‘normal.’

Keep a log: note your mood, energy, weight, and any symptoms. Bring it to every appointment. Your doctor needs to see the full picture. Lithium isn’t a drug you take and forget. It’s a long-term partnership-with your brain, your thyroid, and your health team. Manage it well, and you can live a stable, full life-even with a thyroid that needs a little extra care.