Lithium Carbonate Side Effects: What to Expect and When to Call Your Doctor

Lithium Carbonate is a highly effective mood stabilizer with more than 70 years of clinical history—but it is also one of the few psychiatric medications with a boxed (black box) warning for toxicity. Understanding its side effects, knowing which ones are expected, and recognizing the early signs of toxicity could prevent a serious medical emergency. This guide covers everything patients need to know.

The Boxed Warning: Lithium Toxicity

Lithium's FDA-approved labeling carries a boxed warning—the FDA's most serious safety warning—for toxicity. The key message: the toxic level of lithium is very close to the therapeutic level. The therapeutic range is 0.8–1.2 mEq/L for acute treatment and 0.6–1.2 mEq/L for maintenance. Toxicity can begin at levels of ≥1.5 mEq/L—just slightly above the target range. This is why regular blood level monitoring is required throughout therapy.

Common Side Effects That Many Patients Experience

These side effects are common, especially when first starting lithium or after a dose increase. They are not necessarily signs of toxicity and often improve over time:

Fine hand tremor: A slight shaking of the hands is very common, especially in the first weeks of therapy. Often improves with time or with dose adjustment.

Increased thirst and urination: Lithium causes polyuria (increased urination) and polydipsia (increased thirst). Stay well-hydrated. Avoid dramatic fluid restriction.

Nausea and diarrhea: Especially common when starting therapy. Taking lithium with food can significantly reduce GI upset.

Weight gain: Modest weight gain (5–10 lbs) is common during long-term therapy. Dietary awareness and physical activity can help manage this.

Memory and cognitive effects: Some patients report mild cognitive dulling, difficulty concentrating, or memory issues. This may improve at lower doses.

Hair thinning: Diffuse hair thinning occurs in some patients. This may be related to lithium-induced thyroid changes; check your TSH.

Acne or skin changes: Lithium can worsen acne or exacerbate psoriasis in susceptible patients.

Early Warning Signs of Lithium Toxicity — Call Your Doctor

Contact your prescriber promptly if you experience any of the following. These can be early signs that your lithium level is drifting too high:

Worsening or coarser tremor (not just a fine hand shake)

Lightheadedness, lack of coordination, unsteady gait

Excessive drowsiness or confusion

Muscle weakness or twitching

Blurred vision or ringing in the ears (tinnitus)

Slurred speech

Severe Toxicity — Call 911 or Go to the Emergency Room

These are signs of severe lithium toxicity requiring immediate emergency care:

Seizures

Profound confusion or delirium

Loss of consciousness or coma

Irregular heartbeat or chest pain

Things That Raise Lithium Levels—and Your Risk of Toxicity

Certain situations can cause your lithium levels to rise without any change in your dose. Alert your doctor if any of these apply:

Starting an NSAID (ibuprofen, naproxen, etc.): NSAIDs reduce renal lithium clearance and can raise levels by 30–50% or more. Never start an OTC NSAID without telling your prescriber first.

Dehydration: Hot weather, vomiting, diarrhea, or excessive sweating can concentrate lithium levels. Maintain good fluid and salt intake.

Low-sodium diet: Lithium and sodium compete in the kidneys. A sudden drop in sodium intake (low-salt diet, significant dietary change) can cause lithium retention and toxicity.

New diuretic or ACE inhibitor/ARB: These blood pressure medications significantly raise lithium levels. If your cardiologist or PCP prescribes a new blood pressure medication, inform your psychiatrist immediately.

Long-Term Side Effects to Monitor

Kidney function: Long-term lithium use can affect kidney function. Your doctor will monitor creatinine, BUN, and eGFR every 6 months. Risk increases with duration of therapy.

Thyroid function: Hypothyroidism develops in up to 40% of patients on long-term lithium. TSH should be checked every 6–12 months. If you develop fatigue, weight gain, cold intolerance, or hair loss, ask about thyroid testing.

Calcium levels: Lithium can cause hypercalcemia and hyperparathyroidism. Serum calcium should be checked annually.

For a detailed guide to drug interactions that affect lithium levels, see Lithium Carbonate Drug Interactions: What to Avoid and What to Tell Your Doctor. To learn more about the medication, see What Is Lithium Carbonate? Uses, Dosage, and What You Need to Know.