Which of the following is an early indication of lithium toxicity?

• A. Tremor
• B. Polyuria
• C. Nausea
• D. Weight gain

Answer: (B)

When lithium levels begin to rise, the first noticeable change is often a fine tremor. This motor sign reflects CNS effects from lithium and tends to appear before more severe toxicity such as confusion or ataxia. It serves as an early warning that serum levels may be increasing and that rehydration status and drug interactions should be reviewed.

Polyuria, while common with lithium use due to its effect on kidney response to ADH, is a frequent side effect rather than a specific early indicator of toxicity. It can occur at therapeutic levels and doesn’t by itself signal rising toxicity. Nausea and weight gain can occur with lithium, but they are less specific to early toxicity; nausea may accompany higher levels, and weight gain tends to develop with longer-term use rather than as an early toxicity sign.

In short, the earliest and most characteristic warning sign to watch for is tremor, prompting evaluation of lithium level, hydration status, and potential interacting medications.