Background Lithium carbonate is widely used as a first-line therapeutic agent for the depressive and manic phases of bipolar disorder. Although limb tremors and hypothyroidism are well-known side effects of lithium carbonate, other rare adverse reactions can also occur. Case presentation A 53-year-old Japanese woman diagnosed with lithium intoxication developed dysgeusia and glossalgia during treatment with lithium carbonate. She also showed symptoms of a swaying gait, finger tremors, and dysarthria. All of these symptoms subsided when her blood lithium concentration was reduced to a level below that which induces intoxication. Conclusions We present a rare case of lithium carbonate–induced dysgeusia accompanied by glossalgia. Early detection of these symptoms is important in clinical settings because they can be overlooked until patients lose their appetite, which severely impairs their quality of life.

Typical antipsychotics were first developed in the 1950s and have been used to treat psychosis. However, their side effects, such as extrapyramidal symptoms, hyperprolactinemia, negative symptoms, and cognitive decline, have been considered to be problematic. Atypical antipsychotics are commonly used because they have fewer extrapyramidal symptoms than typical antipsychotics, and are effective in improving symptoms of schizophrenia and bipolar disorder. Side effects of these atypical antipsychotics include impaired glucose tolerance and weight gain. In some cases, the onset of diabetes and ketoacidosis may force patients to stop taking these drugs.Lurasidone is categorized as an atypical antipsychotic and is effective for patients with acute bipolar I depression and schizophrenia. Common side effects of lurasidone include nausea, akathisia, drowsiness, and vomiting. Because lurasidone is considered to have fewer metabolic adverse effects than other antipsychotics, it is recommended as an alternative when other antipsychotics considerably increase body weight or blood sugar concentrations. 1 We report here a rare case of hyperosmolar hyperglycemic syndrome as a side effect of lurasidone. Because hyperosmolar hyperglycemic syndrome has a high mortality rate, its early detection and treatment are critical.