Which of the following can be an adverse effect of lithium?

• A. Increased urination
• B. Bradycardia
• C. Rash
• D. Hearing loss

Answer: (A)

The key idea here is that lithium frequently affects the kidneys, specifically by reducing the kidney’s ability to concentrate urine. This happens because lithium can cause nephrogenic diabetes insipidus, where the collecting ducts don’t respond properly to antidiuretic hormone. As a result, the kidneys pass large amounts of dilute urine, so polyuria (increased urination) occurs. This is one of the most common and characteristic adverse effects of lithium.

Other options don’t fit as well with lithium’s typical adverse profile. Bradycardia isn’t a hallmark effect of lithium and would more likely be seen with other heart-related medications. Rash can happen with many drugs but is not a classic or defining adverse effect of lithium, and hearing loss is not a typical lithium-related toxicity.

In practice, if someone on lithium develops polyuria, clinicians consider whether it’s nephrogenic DI from the drug, ensure adequate hydration, and monitor renal function and lithium levels, since dehydration can raise lithium levels and risk toxicity.