What is the therapeutic serum range for lithium?

• A. 0.2-0.4 mmol/L
• B. 0.6-0.8 mmol/L
• C. 1.0-1.2 mmol/L
• D. 1.5-2.0 mmol/L

Answer: (B)

Lithium has a very narrow therapeutic index, so keeping its serum concentration within a safe window is essential to control symptoms while minimizing toxicity. For maintenance in bipolar disorder, the target is commonly around 0.6 to 0.8 mmol/L (which is the same as mEq/L for lithium). This range sits comfortably within the therapeutic zone and avoids being too low to be effective or too high to risk adverse effects. Higher levels, such as 1.0–1.2 mmol/L, can be therapeutic for some patients but come with a greater risk of toxicity, and levels above about 1.5–2.0 mmol/L are associated with significant toxicity (nausea, tremor, confusion, ataxia, renal effects). Subtherapeutic ranges like 0.2–0.4 mmol/L are unlikely to provide mood stabilization. Hence, 0.6–0.8 mmol/L is the best standard target.