When you take lithium, a mood-stabilizing medication commonly prescribed for bipolar disorder. Also known as lithium carbonate, it helps prevent extreme mood swings—but it doesn’t come without trade-offs. One of the most common and often overlooked side effects is its impact on the thyroid, a small gland in your neck that controls metabolism, energy, and body temperature. Many people on long-term lithium therapy develop hypothyroidism, a condition where the thyroid doesn’t make enough hormones, leading to fatigue, weight gain, and brain fog.
Lithium doesn’t destroy your thyroid. Instead, it interferes with how the gland releases hormones. It blocks iodine uptake and disrupts the production of T3 and T4, the two main thyroid hormones. This isn’t rare—studies show up to 20% of people on lithium develop some form of thyroid dysfunction, and about 5-15% end up with full-blown hypothyroidism. The risk goes up the longer you take it, especially if you’re female or have a family history of thyroid issues. Your doctor should check your thyroid levels before you start lithium, then again every 6 to 12 months after. If your TSH (thyroid-stimulating hormone) starts creeping up, it’s a red flag. Left untreated, low thyroid function can make your mood symptoms worse, which defeats the whole purpose of taking lithium in the first place.
Here’s the good news: hypothyroidism from lithium is usually easy to fix. Most people just need a daily dose of levothyroxine, the same medication used for underactive thyroid from other causes. You don’t have to stop lithium. You don’t have to quit your treatment. You just need regular blood tests and the right dose of thyroid hormone. Some people even notice their energy and focus improve once their thyroid levels are back in range. But you won’t know unless you get tested. If you’re on lithium and feel unusually tired, gain weight without trying, or struggle with memory problems, don’t brush it off as stress or aging. Ask for a TSH and free T4 test. It’s a simple blood draw—and it could change how you feel every day.
The posts below cover real-world cases and comparisons of how lithium interacts with other medications, what lab values matter most, and how to manage thyroid health without sacrificing mood stability. You’ll find practical advice from people who’ve been there, and clear guidance on what to ask your doctor next.
