When you take lithium, a mood-stabilizing medication primarily used for bipolar disorder. Also known as lithium carbonate, it helps prevent manic and depressive episodes—but it doesn’t come without trade-offs. One of the most common and often overlooked side effects is how it affects your thyroid, a small gland in your neck that controls metabolism, energy, and mood. Many people start lithium without realizing it can slow down thyroid function, leading to hypothyroidism, a condition where your thyroid doesn’t make enough hormones. This isn’t rare—it happens in up to half of long-term users.
Here’s how it works: lithium interferes with the thyroid’s ability to release stored hormones and blocks iodine uptake, which is essential for hormone production. Over time, your thyroid may struggle to keep up, and your body starts showing signs: constant tiredness, weight gain, cold hands, dry skin, brain fog, or even depression that feels worse than before you started lithium. These symptoms are easy to blame on your bipolar disorder, but they might actually be your thyroid crying for help. Blood tests like TSH, T3, and T4 are the only way to know for sure. Most doctors check these before starting lithium and then every 6 to 12 months after—but if you feel off, don’t wait. Ask for a repeat test.
Good news: you don’t have to quit lithium if your thyroid slows down. In most cases, doctors simply add a low dose of levothyroxine, a synthetic thyroid hormone replacement to balance things out. It’s safe, effective, and often keeps people on lithium without side effects. Stopping lithium because of thyroid issues isn’t usually needed—it’s like fixing a flat tire without ditching the car. The key is catching it early. If you’ve been on lithium for more than a year and feel like you’ve lost your spark, talk to your doctor about your thyroid. It’s not weakness. It’s biology.
What you’ll find below are real, practical comparisons and guides from people who’ve walked this path. From how lithium stacks up against other mood stabilizers in terms of thyroid impact, to what lab numbers actually mean, to how to spot the quiet signs your thyroid is struggling—these posts give you the tools to stay in control. No fluff. Just what works.
