Ms. A was a 26-year-old single white woman with diagnoses of bipolar disorder and alcohol dependence; the latter was in early full remission. For 5 months she had been stable while taking 900 mg b.i.d. of lithium, 2 mg b.i.d. of risperidone, 20 mg b.i.d. of propranolol, 0.5 mg b.i.d. of lorazepam, 100 mg/day of sertraline, and 25 mg b.i.d. of hydroxyzine. Her lithium level on this drug regimen was 1.1 mmol/liter.

Ms. A came to the emergency room complaining of "dizziness," "grogginess," and loose stools over the several days since she had begun taking an over-the-counter medication (containing chlorpheniramine, pseudoephedrine, and acetaminophen) for sinus problems. She had stopped taking this medication 2 days before her emergency room visit because of these symptoms. She reported using no other nonprescribed medications, alcohol, or drugs. Her vital signs and the results of a physical examination were normal. She left the emergency room before an ECG was performed or any laboratory work was completed because of anxiety.

Ms. A was seen the next day for a scheduled psychiatric clinic visit and again reported feeling "groggy" but better since she had stopped taking the sinus medication. She was alert and oriented and had no tremor. Again she reported no use of any medications other than those previously mentioned. Two days later, Ms. A returned to the emergency room with complaints of nausea, diarrhea, an unsteady gait, tremor, and drowsiness. At this visit she reported that she had been taking an over-the-counter preparation of herbal diuretics for the past 2–3 weeks for weight loss. She was drowsy but oriented and had a coarse tremor, an unsteady gait, and nystagmus. She was admitted to the coronary care unit with a lithium level of 4.5 mmol/liter.