Lithium Thyroid Monitoring: What You Need to Know About Thyroid Health on Lithium

When you take lithium, a mood-stabilizing medication commonly used for bipolar disorder. Also known as lithium carbonate, it helps control extreme mood swings—but it can also quietly affect your thyroid, a small gland in your neck that controls metabolism, energy, and mood.

Up to half of people on long-term lithium develop some level of thyroid dysfunction. It’s not always obvious. You might feel more tired than usual, gain weight without changing your diet, or notice your mood slipping—even if your bipolar symptoms are under control. That’s why lithium thyroid monitoring, regular blood tests to check thyroid hormone levels while on lithium isn’t optional. It’s a basic safety step, like checking your blood pressure if you’re on blood pressure meds. Doctors usually test TSH, free T4, and sometimes thyroid antibodies within the first few months of starting lithium, then at least once a year after that. If your thyroid starts underperforming, it’s often fixable with a simple daily pill—levothyroxine—without stopping lithium.

Some people worry that thyroid changes mean lithium isn’t working. That’s not true. Lithium doesn’t stop being effective when your thyroid dips. In fact, treating the thyroid issue often makes your mood stabilize even better. Skipping these tests? That’s where things get risky. Untreated hypothyroidism can lead to depression, brain fog, heart problems, and even worsen bipolar symptoms. And if you’re older, female, or have a family history of thyroid disease, your risk goes up. You don’t need to guess. Just ask your doctor for a TSH test every year—or every six months if you’ve had issues before. Keep a log of how you feel: energy levels, weight, mood, cold sensitivity. That info helps your doctor connect the dots faster.

What you’ll find below are real, practical guides from people who’ve been there. You’ll read about how thyroid tests are done, what the numbers mean, how to talk to your doctor when results look odd, and why some people need to switch to a different mood stabilizer—not because lithium failed, but because their thyroid couldn’t keep up. These aren’t theory pieces. They’re lived experiences, backed by medical evidence, and written for people who just want to stay healthy while taking what works.