A nurse is reviewing discharge instructions with a client who has bipolar disorder and is taking lithium. Which of the following manifestations should the nurse include as an indication of mild toxicity?

Choice A reason: Urinary retention is not a typical manifestation of lithium toxicity. Lithium more commonly causes polyuria due to nephrogenic diabetes insipidus. Choice B reason: Hyperactivity is a symptom of mania, not lithium toxicity. Lithium is used to control hyperactivity, not cause it. Choice C reason: Constipation is not a hallmark sign of lithium toxicity. Gastrointestinal upset such as diarrhea is more typical. Choice D reason: Muscle weakness is a sign of mild lithium toxicity. It reflects neuromuscular impairment due to lithium’s effect on nerve conduction and muscle function. This is the correct answer.