Lithium Thyroid Side Effects: What You Need to Know

When you take lithium, a mood-stabilizing medication used primarily for bipolar disorder. It's known for helping control extreme mood swings, but it also quietly affects other parts of your body—especially your lithium carbonate. One of the most common and often overlooked issues is how lithium interacts with your thyroid, a small gland in your neck that controls metabolism, energy, and mood. About 20% of people on long-term lithium develop some form of thyroid problem. It’s not rare. It’s expected. And if you don’t watch for it, it can make you feel worse than the condition you’re treating.

Lithium doesn’t destroy your thyroid. It just messes with how it works. It blocks the release of thyroid hormones, which can lead to hypothyroidism, a condition where your body doesn’t make enough thyroid hormone. Symptoms are easy to miss because they look like depression: fatigue, weight gain, cold hands, brain fog, dry skin, or low mood. If you’re already on lithium for bipolar disorder, it’s hard to tell if your low energy is from your illness or your thyroid. That’s why regular blood tests—TSH and free T4—are non-negotiable. Doctors check these every 6 to 12 months, sometimes more often when you start or change your dose.

Some people develop a goiter—a visible swelling in the neck—without any hormone changes. That’s usually harmless but can be unsettling. In rare cases, lithium triggers autoimmune thyroiditis, where your immune system attacks your thyroid. This isn’t an allergy. It’s a chemical effect. And unlike some side effects, this one doesn’t go away just because you stop taking lithium. Sometimes your thyroid needs lifelong replacement with levothyroxine. But here’s the good news: if caught early, thyroid issues from lithium are easy to fix. You don’t have to quit lithium. You just need to monitor and treat the thyroid separately.

People on lithium often don’t realize their symptoms are thyroid-related. They blame stress, aging, or their mental health. But if you’ve been on lithium for more than a year and feel off, ask for a thyroid panel. Don’t wait for your doctor to bring it up. Bring it up yourself. Bring your list of symptoms. Bring your medication log. This isn’t about being difficult—it’s about staying well.

The posts below cover real cases, lab results, and practical tips from people managing lithium and thyroid health together. You’ll find advice on testing schedules, what to ask your endocrinologist, how to spot early warning signs, and how to talk to your psychiatrist about balancing mood stability with thyroid function. This isn’t theory. It’s what works for people taking lithium every day.