Lithium and Hypothyroidism: What You Need to Know About the Connection

When you take lithium, a mood-stabilizing medication commonly used for bipolar disorder. It's known for helping control extreme mood swings, but it doesn't come without trade-offs. One of the most common, yet often overlooked, side effects is its impact on your thyroid, a small gland in your neck that controls metabolism, energy, and mood. Over time, lithium can interfere with how your thyroid makes hormones, leading to hypothyroidism, a condition where your thyroid doesn't produce enough hormones. This isn’t rare—studies show up to 20% of people on long-term lithium develop some level of thyroid dysfunction.

Why does this happen? Lithium blocks the release of thyroid hormones and can reduce the gland’s ability to take up iodine, which it needs to function. You might not feel anything at first, but over months or years, symptoms like fatigue, weight gain, cold intolerance, dry skin, or even depression can creep in. And here’s the catch: these symptoms can look a lot like your original condition. That’s why doctors check your thyroid levels—TSH, T3, T4—before you start lithium and at least once a year after. If your TSH starts creeping up, it’s a red flag. Catching it early means you can often fix it with a simple daily pill: levothyroxine. You don’t have to stop lithium. Most people keep taking it, just add a thyroid hormone replacement.

This isn’t just about physical health. Your mood can swing if your thyroid dips too low. People on lithium who develop untreated hypothyroidism often report feeling more sluggish, down, or emotionally flat—even if their bipolar symptoms were under control. That’s why monitoring isn’t optional. It’s part of the treatment plan. And if you’ve been on lithium for years and suddenly feel off, don’t assume it’s your mental health. Get your thyroid checked. It’s a quick blood test that could explain everything.

The good news? You’re not alone. Many people manage both lithium and hypothyroidism successfully for decades. The key is awareness, regular tests, and open communication with your care team. You don’t need to choose between stability and health—you can have both, if you stay on top of it.

In the posts below, you’ll find real-world insights on how lithium affects your body, what labs to track, how to tell if your symptoms are from your thyroid or your mood disorder, and what alternatives or adjustments might help. This isn’t theory. It’s what people actually experience—and what works.