A nurse is teaching a client who has bipolar disorder about lithium. Which of the following statements should the nurse include in the teaching?

Choice A reason: Monitoring lithium levels is essential because of its narrow therapeutic index; toxicity can occur if levels rise slightly above the therapeutic range. Choice B reason: Weight gain is not an indication of lithium toxicity; instead, toxicity signs include tremors, nausea, diarrhea, and confusion. Choice C reason: Lithium is not addictive, and therapy is often long-term to prevent relapse of mood episodes. Choice D reason: Diuretics are contraindicated with lithium because they increase the risk of toxicity by altering sodium and fluid balance.