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

Lithium is one of the most effective long-term treatments for bipolar disorder. It reduces the frequency and severity of manic and depressive episodes better than almost any other medication. But for many people taking it, there’s a hidden cost: your thyroid. About 1 in 5 people on lithium develop hypothyroidism. Some get goiters. A few even develop hyperthyroidism. And if you don’t know what to watch for, these problems can sneak up on you - leaving you tired, gaining weight, or feeling worse than before you started treatment.

How Lithium Breaks Down Thyroid Function

Lithium doesn’t just float through your body. It targets your thyroid gland directly. It blocks the release of thyroid hormones by interfering with how thyroglobulin - the protein that holds thyroid hormones together - gets broken down. It also stops iodine from being used properly to make new hormones. On top of that, it reduces how much T4 (the main thyroid hormone) gets converted into T3 (the active form your body uses). The result? Your thyroid can’t keep up, even if it’s working hard.

Over time, this leads to swelling - goiters. Studies show 30% to 59% of people on long-term lithium develop them. In places like Denmark, where iodine intake is lower, rates climb even higher. In the U.S., where iodized salt is common, it’s still around 30-40%. Women under 60 are three times more likely to develop thyroid issues than men on the same dose. And the longer you’re on lithium, the higher your risk. After 10 years, nearly half of users show signs of thyroid dysfunction.

What Happens to Your Thyroid Numbers

Most people on lithium don’t get hyperthyroidism. That’s rare - only 3-5% of cases. When it does happen, it’s usually painless thyroiditis, not Graves’ disease. Your thyroid leaks hormones temporarily, then settles down. But hypothyroidism? That’s the real issue. About 20-32% of people on lithium end up with low thyroid hormone levels. TSH - the hormone your pituitary gland releases to tell your thyroid to work harder - climbs. Sometimes it hits 8 or 10. Normal is under 4.5.

Here’s the catch: it doesn’t happen right away. It takes 6 to 8 weeks for TSH to rise after starting lithium. Many doctors panic and stop the lithium too soon because of an early, mild TSH spike. A 2022 study found that 23% of primary care doctors discontinued lithium because of this. But if you wait, the numbers often stabilize. That’s why guidelines say: monitor every 6 months for the first year, then yearly if stable.

Lithium vs. Other Mood Stabilizers

Not all mood stabilizers mess with your thyroid the same way. Valproate can cause mild TSH increases in 5-10% of users - usually temporary. Carbamazepine barely touches thyroid function. But lithium? It’s in a different league. It’s the only one that consistently causes structural changes in the thyroid gland itself. And it’s not just about dose. A 2024 study showed that for every 100 mg/day increase in lithium, your odds of worsening thyroid function go up by 27%. That’s a clear dose-response relationship.

Amiodarone, a heart drug, also causes thyroid problems - but for different reasons. It’s loaded with iodine, which overwhelms the gland. Lithium doesn’t add iodine. It jams the system from the inside. That’s why switching from amiodarone to lithium doesn’t solve thyroid issues. They’re different problems.

Managing Hypothyroidism on Lithium

If your TSH rises and your free T4 drops, you’ll likely be started on levothyroxine. But here’s what most people don’t know: if you’re on lithium, you often need 20-30% more levothyroxine than someone without lithium to get your TSH back to normal. That’s because lithium interferes with how your body uses the hormone. So if you’re on 50 mcg and still feel tired, don’t assume it’s just stress. Ask for a blood test. Your dose might need to be bumped up to 60 or 70 mcg.

Don’t stop lithium just because your thyroid is off. The benefits for mood stability are too strong. A 2017 meta-analysis showed lithium reduces the risk of any mood episode by 39% compared to placebo. It also cuts suicide attempts by 14% compared to other mood stabilizers. That’s huge. The goal isn’t to avoid thyroid problems - it’s to manage them while keeping your mood stable.

What About Hyperthyroidism?

If you suddenly feel anxious, lose weight, have a rapid heartbeat, or feel hot all the time, get your thyroid checked. But don’t jump to conclusions. Most cases of lithium-induced hyperthyroidism are painless thyroiditis - not Graves’ disease. It usually clears up on its own in 3 to 6 months. You don’t need radioactive iodine or antithyroid drugs like methimazole unless it’s confirmed to be Graves’.

If it is Graves’ - rare, but possible - you’ll need carbimazole, starting at 20 mg/day. Steroids might be added if inflammation is high. But again, don’t rush to stop lithium. Many patients stay on both lithium and carbimazole for months while their thyroid resets. Stopping lithium can even make things worse. One case report described a thyroid storm - a life-threatening surge of hormones - after someone had lithium removed via dialysis. That’s why sudden discontinuation is dangerous.

Who’s Most at Risk?

Not everyone on lithium gets thyroid problems. But certain people are more likely to:

• Women under 60
• People with a family history of autoimmune thyroid disease
• Those with high baseline TSH before starting lithium
• People taking other medications like gabapentin or pregabalin
• Those living in low-iodine regions (though even in iodine-sufficient areas, risk remains)

Autoimmune antibodies (like TPO antibodies) are found in more people on lithium than in the general population - but not always. Some studies say yes, others say no. The truth? Lithium may trigger thyroid issues in people already genetically predisposed. It doesn’t create autoimmunity out of thin air. It just lights the fuse.

New Tools for Better Management

There’s good news on the horizon. A 2024 study developed a predictive model that looks at your age, gender, baseline TSH, and other meds to estimate your risk of thyroid decline. It’s 82% accurate. That means doctors can now spot high-risk patients early and start monitoring closer.

Another promising option: selenium. A 2023 randomized trial gave 100 mcg of selenium daily to lithium users. After two years, only 14% developed hypothyroidism - compared to 24% in the placebo group. That’s a 42% reduction. Selenium helps protect the thyroid from oxidative stress. It’s cheap, safe, and easy to add. Ask your doctor if it’s right for you.

And in the future, new lithium-like drugs are being tested. RG101, currently in Phase II trials, looks just as good for mood control but doesn’t raise TSH. If it works, it could replace lithium for many people - but it’s still years away.

What You Should Do Right Now

If you’re on lithium, here’s your action plan:

1. Get a full thyroid panel before you start - TSH, free T4, free T3, and TPO antibodies.
2. Check every 6 months for the first year, then yearly after that.
3. If TSH is over 4.5, don’t panic. Wait 2-3 months and retest. Don’t rush to stop lithium.
4. If you’re diagnosed with hypothyroidism, start levothyroxine. Expect to need a higher dose than average.
5. Ask about selenium (100 mcg/day) as a preventive step.
6. Never stop lithium suddenly. Talk to your psychiatrist first.
7. Track your symptoms: fatigue, weight gain, cold intolerance, brain fog - these are signs your thyroid might be struggling.

One patient on Reddit wrote: ‘My TSH went from 1.8 to 8.7 in 18 months. I take 75 mcg levothyroxine now. My psychiatrist won’t lower my lithium dose. But I’m stable. I’d rather be on both than go back to mania.’ That’s the reality for many. Lithium isn’t perfect. But for people with bipolar disorder, it’s often the best tool they have. The key isn’t avoiding side effects - it’s managing them smartly.

Is Lithium Still Worth It?

Yes. Despite the thyroid risks, lithium remains first-line treatment for bipolar disorder in 78% of global treatment guidelines. It’s the only mood stabilizer proven to reduce suicide risk long-term. Newer drugs like quetiapine or lurasidone help with symptoms, but none match lithium’s ability to prevent relapse over decades.

The trade-off is real. You’ll need lifelong monitoring. You might need thyroid medication. You might feel tired even after treatment. But for most people, the trade-off is worth it. Your mood stability is worth more than the extra pill you take each morning.

Final Thoughts

Lithium isn’t a perfect drug. But it’s one of the few that can truly change the trajectory of bipolar disorder. The thyroid issues are real, predictable, and manageable. You don’t have to choose between mental stability and physical health. With regular monitoring, smart dosing, and simple additions like selenium, you can stay on lithium for decades - and still feel good.

It’s not about avoiding side effects. It’s about staying ahead of them.