Valproic acid is a broad-spectrum drug used in neurological disorders but also in psychiatric disorders such as mood stabilizer in bipolar or schizoaffective disorders.

Despite being a usually well tolerated drug, valproic acid may be associated with some adverse effects. Most of which are mild and transient, however some adverse reactions may be serious like encephalopathy. In fact, valproic acid induced encephalopathy is an unusual but serious complication, characterized by decreasing level of consciousness, focal neurological deficits, cognitive slowing, vomiting, drowsiness and lethargy, with or without hyperammonemia.

The aim of this work is to describe a case report of a woman who developed valproic acid induced encephalopathy during her hospitalization in the Coimbra's Psychiatric Department.

This is a woman, 46 years old, diagnosed with a bipolar disorder who was hospitalized for stabilization of their depressive symptoms.

At the entrance, a confusional state was found with fluctuating state of consciousness, psychomotor slowing and incoherent speech.

An analytical study was conducted which showed a hyperammonemia of 70μg/ dL.

Immediately the valproic acid was suspended on suspicion of encephalopathy induced by this drug.

Gradually, in about 2 or 3 weeks, confusional state disappeared, and the patient discharged from the hospital oriented in time and space, with coherent speech, euthymic mood and regularized sleep.

Valproic acid induced encephalopathy, is a reversible but potentially fatal adverse reaction that requires a high index of suspicion. Organic brain damage and polytherapy appear to be important risk factors for its occurrence.