Does Lithium Cause Hypothyroidism? What to Know

Lithium has been a workhorse medication for bipolar disorder for decadesreliable, effective, and occasionally a bit like that friend who shows up early, helps you move, and then “accidentally” breaks a lamp. One of lithium’s best-known “oops” moments is its impact on the thyroid gland.

The short version: yes, lithium can contribute to hypothyroidism (an underactive thyroid) in some people. The good news is that thyroid changes are usually predictable, testable, and treatableand many patients can stay on lithium while managing thyroid function.

Quick Answer: Can Lithium Cause Hypothyroidism?

Yes. Lithium can interfere with normal thyroid function and increase the risk of hypothyroidism. The risk isn’t the same for everyone, and not everyone who takes lithium will develop thyroid problems. But it’s common enough that routine thyroid monitoring is a standard part of lithium care.

Why the Thyroid Cares About Lithium

Your thyroid is a small gland in your neck that helps regulate metabolism, energy, temperature tolerance, heart rate, and a bunch of other behind-the-scenes processes. It uses iodine to make thyroid hormones (mainly T4 and T3), and your pituitary gland helps manage the process using TSH (thyroid-stimulating hormone).

Lithium tends to “hang out” in the thyroid. Once it’s there, it can disrupt thyroid hormone production and release in a few ways:

• It may reduce iodine uptake (your thyroid’s raw material for hormone production).
• It can interfere with hormone synthesis (how the gland builds thyroid hormones).
• It can inhibit release of thyroid hormones into the bloodstream, which is a key pathway leading to hypothyroidism and goiter.

Think of it like this: your thyroid is a factory. Iodine is the supply delivery. T4/T3 are the products. Lithium can mess with the delivery trucks, the assembly line, and the shipping departmentso output drops and your body complains.

How Common Is Lithium-Related Hypothyroidism?

Estimates vary depending on the population studied (age, sex, baseline thyroid health, length of lithium therapy, and how aggressively labs are monitored). Across studies and reviews, hypothyroidism is consistently recognized as one of the more frequent endocrine side effects of lithium, and a meaningful subset of long-term users end up needing thyroid hormone replacement.

It’s also worth noting that thyroid changes can be:

• Overt hypothyroidism: thyroid hormone levels are low and symptoms may be more noticeable.
• Subclinical hypothyroidism: TSH is elevated but thyroid hormone levels may still be in range, and symptoms can be mild or absent.

Who’s Most at Risk?

Lithium doesn’t play favoritesbut some people are more likely to develop hypothyroidism while taking it. Risk tends to be higher if you have:

• Pre-existing thyroid issues (even mild or “borderline” findings before lithium starts)
• Thyroid autoimmunity (like Hashimoto’s thyroiditis or thyroid antibodies)
• A family history of thyroid disease
• Female sex (many studies show higher rates in women)
• Longer duration of lithium therapy
• Older age (thyroid disease becomes more common with age in general)

There’s a practical takeaway here: lithium isn’t automatically “bad for your thyroid,” but it can expose a thyroid that was already struggling quietly in the backgroundlike turning up the music and suddenly noticing a speaker is blown.

Signs and Symptoms: What Hypothyroidism Feels Like

Hypothyroidism can be sneaky. Some symptoms overlap with depression, burnout, chronic stress, or the “I’m a human in late-stage capitalism” experience. That’s why lab testing matters.

Common symptoms of an underactive thyroid

• Fatigue or low energy that doesn’t match your sleep
• Weight gain or difficulty losing weight (even with no major lifestyle change)
• Feeling cold more easily
• Dry skin, hair changes, or thinning hair
• Constipation
• Brain fog, slowed thinking, low motivation
• Low mood or worsening depression
• Heavier or irregular menstrual cycles
• Slower heart rate
• Puffy face or hoarseness (in some cases)

Important note: lithium itself can cause side effects (like weight changes or fatigue) that resemble hypothyroidism. So if symptoms show up, it’s not always obvious which “villain” is responsibleagain, labs help sort it out.

How Doctors Test for Lithium-Related Thyroid Issues

The cornerstone tests are typically:

• TSH (often the most sensitive early signal)
• Free T4 (to confirm whether thyroid hormone levels are actually low)

Many clinicians also consider thyroid antibodies (like TPO antibodies) if autoimmune thyroid disease is suspected, especially if TSH starts trending upward or there’s a strong family history.

Monitoring schedule: what’s typical?

While exact schedules vary, a common approach is:

• Baseline thyroid tests before starting lithium
• Repeat testing during the first months (because early shifts can happen)
• Ongoing monitoring every 6–12 months for stable patients, or more often if results change or symptoms appear

If you’re thinking, “Wow, that’s a lot of blood tests,” you’re not wrong. But this is one of the reasons lithium can be used safely long-term: issues are usually caught early through routine monitoring rather than waiting for a dramatic symptom crash.

What Happens If Your TSH Goes Up on Lithium?

If a lab result shows elevated TSH, your clinician will typically look at the full picture:

• Are you having symptoms?
• What is your free T4 doing?
• Is this a one-time blip or a consistent trend?
• Are there other factors (illness, pregnancy/postpartum status, medication changes)?

Possible next steps

• Repeat labs after a short interval to confirm the change.
• Watchful waiting for mild/subclinical cases with no symptoms (not always, but sometimes).
• Start thyroid hormone replacement (commonly levothyroxine) if hypothyroidism is confirmed or symptoms are significant.
• Coordinate psychiatric + medical care so mood stability stays front and center.

The key point: developing hypothyroidism on lithium does not automatically mean lithium must be stopped. In many cases, treating the thyroid problem is enough to keep both your mood and metabolism on speaking terms.

Can You Stay on Lithium If You Develop Hypothyroidism?

Often, yes. Many patients continue lithium successfully while taking thyroid hormone replacement. This matters because lithium can be uniquely effective for some peopleespecially those who respond well to it after struggling with other mood stabilizers.

Decisions are individualized. If lithium is providing strong mood stability, clinicians frequently aim to preserve that benefit while managing thyroid function medically. If thyroid dysfunction is severe, difficult to control, or accompanied by other complications, a medication change may be discussed.

One safety reminder: do not stop lithium suddenly without medical guidance. Abrupt changes can increase relapse risk for mood episodes and create more problems than they solve.

Does Lithium Cause Goiter Too?

It can. Goiter is an enlargement of the thyroid gland. If lithium reduces thyroid hormone release, the pituitary may respond by increasing TSH to “push” the thyroid harder. Over time, that extra stimulation can contribute to thyroid enlargement in some people.

Goiter doesn’t always mean severe dysfunction, but it’s a reason clinicians may do a physical neck exam and, in some cases, order a thyroid ultrasoundespecially if there’s visible swelling, swallowing discomfort, or abnormal exam findings.

Could Lithium Ever Cause Hyperthyroidism?

Rarely, yes. While hypothyroidism is the more typical concern, cases of hyperthyroidism have been reported. Because it’s less common, it’s not usually the headline riskbut it’s one more reason routine thyroid monitoring is part of lithium care.

Practical Tips If You Take Lithium

1) Learn your “baseline” symptoms

Before lithium (or early in treatment), note your normal energy, weight patterns, temperature tolerance, and mood baseline. That makes it easier to spot meaningful changes later.

2) Don’t ignore the “soft” symptoms

Fatigue, brain fog, constipation, and dry skin aren’t always dramatic, but they can be the early rumblings of thyroid shiftsespecially when they persist.

3) Ask what labs are being checked and when

A simple question“Are we checking TSH and free T4 regularly?”can prevent months of guessing.

4) Keep the goal clear: stable mood and stable thyroid

This isn’t an either/or situation for many patients. With good monitoring and treatment, it can be both.

When to Call Your Clinician ASAP

Contact your healthcare provider promptly if you develop:

• Marked fatigue that interferes with daily function
• Rapid or unexplained weight changes
• New neck swelling, hoarseness, or trouble swallowing
• Worsening depression or cognitive slowing
• Any sudden change in symptoms after a lithium dose change

If you feel acutely unwell, confused, severely weak, or notice concerning heart symptoms, seek urgent medical care. (Not everything is thyroid-related, but it’s better to rule out serious causes quickly.)

Real-World Experiences: What People Often Describe (About 500+ Words)

People’s experiences with lithium-related hypothyroidism tend to fall into a few familiar patterns. Not everyone goes through these, and symptoms can vary widelybut if you’ve ever thought, “Is it me, is it the lithium, or is it my thyroid doing interpretive dance again?” you’re not alone.

Experience #1: “I thought my depression was coming back… but it was my thyroid.”

A common story goes like this: someone is doing well on lithiummore stable mood, fewer extremes, better sleepand then, months later, they start feeling heavier and slower. Motivation drops. Brain fog creeps in. They feel emotionally flatter, less sharp, more tired. Because mood symptoms and thyroid symptoms overlap, it’s easy to assume the bipolar disorder is breaking through.

Then labs show an elevated TSH, sometimes with low free T4, and the “mystery relapse” suddenly has a medical explanation. People often describe relief in finally having a reason for what they’re feelingbecause vague fatigue can feel like a personal failure, when it’s actually biology. After thyroid treatment (or sometimes after close monitoring and a plan), many report their energy and mental clarity improving over weeks.

Experience #2: “The scale changed, but my habits didn’t.”

Weight changes can be emotionally loaded. Some people report gradual weight gain that doesn’t match their diet or activity level, and they feel like their body is “not playing fair.” It’s important to be honest here: lithium itself can contribute to weight gain in some individuals, and so can hypothyroidism. When both are on the table, it can feel like you’re fighting a two-headed dragon with a salad.

People often say the most frustrating part is not the number itself, but the uncertainty“What’s causing this, and what can I actually do about it?” That’s why clinicians often emphasize labs and trend tracking instead of guessing. When thyroid levels are corrected, some people find weight becomes easier to manage; others still need a broader plan that accounts for medication effects, sleep, appetite changes, and lifestyle.

Experience #3: “My doctor caught it before I felt anything.”

This is the underappreciated success story of monitoring. Some people feel completely fine, and a routine TSH test shows early thyroid changes. In those cases, clinicians may repeat labs, check free T4, ask about subtle symptoms, and decide whether to observe or treat. Patients often describe this as reassuring: it’s much less scary to hear “we’re watching a number” than to feel miserable for months and then discover the cause.

Experience #4: “I didn’t want to stop lithium because it was finally working.”

This is a big one. Lithium can be a life-changing medication for many people. When thyroid issues show up, patients may worry they’ll lose the stability they fought hard to achieve. A frequent experience is learning that hypothyroidism can often be treated while staying on lithium. That information alone can ease anxiety.

People also report that the best outcomes happen when their psychiatrist and primary care clinician (or endocrinologist) communicate clearlyso thyroid treatment doesn’t unintentionally complicate mood stability, and mood treatment doesn’t ignore physical health. When care is coordinated, many patients feel like they’re finally getting “whole-person” medicine rather than having their body parts treated like separate departments that never email each other.

Experience #5: “The symptoms were subtleuntil they weren’t.”

Hypothyroidism can start quietly: needing more coffee, feeling colder, getting constipated more often, noticing skin dryness, feeling less mentally quick. Many people don’t connect those dots until the cluster becomes obvious. If you recognize yourself here, the takeaway is simple and non-judgmental: subtle symptoms deserve attention, especially when you’re on a medication known to affect thyroid function. Getting a lab check isn’t “overreacting”it’s smart maintenance.

Conclusion

Lithium can cause or contribute to hypothyroidism, but it doesn’t have to be a dealbreaker. The most important tools are regular thyroid testing, awareness of symptoms, and a plan that protects both mood stability and endocrine health. If you’re on lithium and notice changes in energy, weight, cold tolerance, mood, or thinking speed, don’t guesstest. With monitoring and appropriate treatment, many people continue lithium safely and feel well long-term.