Final answer:
The first signs of lithium toxicity are increased thirst and frequent urination. If left untreated, it can lead to more severe symptoms such as nausea, muscle weakness, high blood pressure, and rapid heart rate.
Step-by-step explanation:
The first signs of lithium toxicity include increased thirst and frequent urination. Other symptoms can include feeling very hungry, even though you are eating, and extreme fatigue. If not treated, it can lead to more severe symptoms such as nausea and vomiting, muscle weakness and twitching, high blood pressure, and rapid heart rate.