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

For over 70 years, lithium has been one of the most effective treatments for bipolar disorder. It stabilizes mood, reduces mania, prevents depression, and even lowers suicide risk more than any other medication in its class. But for many people taking it, there’s a hidden cost: their thyroid stops working the way it should.

If you’re on lithium and suddenly feel tired, gain weight, or struggle to stay warm-even when you’re eating well and sleeping enough-your thyroid might be the culprit. About 1 in 5 people on long-term lithium develop hypothyroidism. For some, it’s mild. For others, it’s life-changing. The good news? It’s predictable, manageable, and often reversible. The key is knowing what to watch for-and what to do next.

How Lithium Breaks Your Thyroid (Without Trying To)

Lithium doesn’t attack your thyroid on purpose. It just doesn’t know how to avoid it. The drug works by changing how brain cells communicate, but it also interferes with the tiny, delicate machinery inside your thyroid gland. Specifically, it blocks three critical steps in hormone production:

• It stops iodine from attaching to the protein thyroglobulin, which is needed to make T3 and T4 hormones.
• It prevents the thyroid from breaking down stored hormone to release it into your blood.
• It reduces how well your body converts T4 (the storage hormone) into T3 (the active one).

Over time, this leads to a backup of thyroid tissue. Your thyroid starts to swell-this is called a goiter-and it happens in 30% to 59% of people taking lithium long-term. In some cases, it’s visible. In others, it’s only detectable on an ultrasound. The bigger the goiter, the more likely your thyroid will eventually underproduce hormones.

What makes this worse is that lithium also increases iodine buildup inside the gland. In countries where people get enough iodine in their diet (like the U.S.), this isn’t as big a problem. But in places like Denmark, where iodine levels are lower, goiter rates jump to nearly 50% after 10 years on lithium. Your environment matters as much as your dose.

Who’s Most at Risk?

Not everyone on lithium develops thyroid problems-but some people are far more likely to. Women under 60 are 3.2 times more likely than men to develop hypothyroidism on lithium, even at the same dose. Age matters too: people who start lithium after age 45 have higher rates of thyroid dysfunction than younger users.

Dose is another major factor. For every extra 100 mg per day you take, your risk of worsening thyroid issues goes up by 27%. That doesn’t mean you should drop your dose on your own-lithium is powerful, and lowering it without medical supervision can trigger a relapse. But it does mean your doctor should be watching your dose closely, especially if your TSH levels start creeping up.

And then there’s time. The longer you’re on lithium, the higher your risk. After 1-5 years, about 44% of users develop thyroid changes. After 10 years, that number hits 50%. But here’s the twist: some people’s thyroids adapt. A 2024 study found that while risk rises at first, it slightly decreases over time-suggesting the thyroid may slowly adjust to lithium’s presence.

Hypothyroidism: The Most Common Problem

Most thyroid issues from lithium are hypothyroidism-your thyroid isn’t making enough hormones. Symptoms are easy to miss because they look like depression or just aging:

• Constant fatigue, even after sleeping
• Unexplained weight gain
• Feeling cold when others are fine
• Dry skin and hair loss
• Brain fog or trouble concentrating
• Depression that doesn’t improve with mood meds

One Reddit user with 12 years on lithium wrote: “My TSH went from 1.8 to 8.7 in 18 months. I’m on levothyroxine now, but my psychiatrist won’t lower my lithium dose-even though I’m still exhausted.” That’s not uncommon. Many doctors assume the fatigue is just part of bipolar disorder. But if your TSH is above 4.0 mIU/L (and especially above 5.0), it’s likely lithium’s doing.

Levothyroxine (Synthroid, Tirosint) is the standard treatment. But here’s something many don’t know: people on lithium often need 20-30% more levothyroxine than someone with the same TSH level who isn’t on lithium. Why? Because lithium interferes with how your body uses the replacement hormone. Your doctor needs to check your free T4 levels-not just TSH-to make sure you’re getting enough.

Hyperthyroidism: Less Common, But Dangerous

Only 3-5% of lithium users develop hyperthyroidism, but it’s trickier to handle. It’s rarely Graves’ disease (an autoimmune condition). More often, it’s painless thyroiditis-a temporary inflammation that causes stored hormones to leak out. Symptoms include:

• Rapid heartbeat
• Weight loss despite eating more
• Shakiness or anxiety
• Heat intolerance

Here’s the catch: you don’t treat this with antithyroid drugs like methimazole. In most cases, it resolves on its own within 3-6 months. Beta-blockers can help with symptoms like a racing heart, but the goal is to wait it out. Stopping lithium at this stage can backfire. In rare cases, removing lithium suddenly-even through dialysis-has triggered thyroid storm, a life-threatening surge of thyroid hormone.

If tests show true Graves’ disease (positive antibodies, enlarged thyroid, eye changes), then carbimazole or radioactive iodine may be needed. But that’s uncommon. Most cases are self-limiting.

What Should You Do? A Practical Checklist

Managing lithium and thyroid health isn’t complicated-but it requires consistency. Here’s what works based on current guidelines:

1. Test before you start. Get a full thyroid panel (TSH, free T4, free T3, and thyroid antibodies) before your first lithium dose.
2. Test every 6 months for the first year. After that, annual checks are fine if your levels are stable.
3. Don’t panic at a slightly high TSH. It can take 6-8 weeks for TSH to rise after starting lithium. Don’t jump to conclusions if your first test is borderline.
4. Don’t stop lithium because of thyroid changes. Lithium is more effective than any alternative at preventing suicide and relapse. Managing the thyroid is easier than losing mood control.
5. Ask about selenium. A 2023 trial showed 100 mcg of selenium daily cut hypothyroidism rates by 40% in lithium users. It’s safe, cheap, and not widely known.
6. Track your symptoms. Keep a simple log: energy, weight, mood, temperature sensitivity. Bring it to every appointment.

And if your doctor dismisses your symptoms? Get a second opinion. Endocrinologists who specialize in psychiatric drug side effects know this well. Primary care doctors often don’t.

Alternatives? Yes-but with Trade-offs

Some people ask: “Can I switch to something else?” Valproate and carbamazepine are options, but they’re not better for your thyroid. Valproate causes thyroid issues in 5-10% of users. Carbamazepine barely affects it. But neither matches lithium’s power in preventing suicide.

A 2013 BMJ study showed lithium reduced suicide attempts by 14% more than other mood stabilizers. That’s not a small difference. It’s life-saving. Newer drugs like lamotrigine are gentler on the thyroid but less effective for mania. Quetiapine helps with depression but doesn’t prevent mania as well.

There’s hope on the horizon. A new compound called RG101, currently in Phase II trials, looks like lithium in how it stabilizes mood-but doesn’t raise TSH levels. If it works, it could replace lithium within the next decade. But for now, lithium is still the gold standard.

Real Stories, Real Choices

On Reddit, one user wrote: “I’ve been on 900 mg daily for 8 years. My thyroid is perfect. Every test normal.” That’s real. Not everyone has problems.

Another said: “I gained 30 pounds. My hair fell out. I cried every day-even though I was on levothyroxine. I thought I was failing at being stable. Turns out, I just needed more hormone.”

And a third: “I’d rather be tired and on pills than in the hospital again. Lithium saved my life. I’ll manage the thyroid.”

These aren’t just stories. They’re decisions. Lithium isn’t perfect. But for many, it’s the only thing that keeps them alive and functioning. The thyroid side effects are a price-but one that can be managed with the right care.

If you’re on lithium and your thyroid is acting up, you’re not alone. You’re not broken. You’re not failing. You’re just one part of a complex system that needs careful tuning. And with the right monitoring, the right dose of levothyroxine, and the right doctor, you can keep both your mood and your thyroid in balance.