A male client on lithium reports nausea and blurry vision. What is the most likely cause of these symptoms?

The symptoms of nausea and blurry vision in a male client who is on lithium are most indicative of moderate lithium toxicity. Lithium is a mood stabilizer commonly used to treat bipolar disorder, but it has a narrow therapeutic index, meaning that the difference between an effective dose and a toxic dose is small. As lithium levels increase in the bloodstream, especially above the therapeutic range, patients may begin to experience a variety of symptoms including gastrointestinal disturbances such as nausea and visual disturbances like blurry vision.

In this context, moderate toxicity typically occurs when lithium levels rise above 1.5 mEq/L, which can result in symptoms that range from mild to severe, including gastrointestinal upset, cognitive changes, and visual disturbances. Monitoring lithium levels and awareness of the symptoms of toxicity are crucial for ensuring safe treatment with this medication.

While low blood sugar, dehydration, and drug interactions could potentially lead to similar symptoms, they do not specifically align with the typical adverse effects associated with lithium therapy. Thus, the combination of this client's medication with his reported symptoms strongly points to moderate lithium toxicity as the most likely cause.