To the Editor: St John’s wort (SJW) (Hypericum perforatum) is a natural medicine commonly used for treating depression. We recently encountered a case of an overdose of SJW leading to serious manifestations in the patient.

A 16-year-old girl presented to the emergency department with seizures and confusion. She was intubated and admitted to the intensive care unit. The only relevant history was of febrile convulsions at the age of 4 years. There had been no head trauma.

Results of a computed tomography brain scan and cerebrospinal fluid examination were unremarkable. Electrolyte levels were normal, and standard drug toxicological screens were negative. An electroencephalogram (EEG) confirmed diffuse spike wave activity consistent with generalised epileptic activity.

On further questioning, it was found that she had taken large quantities of SJW — up to fifteen 300 μg tablets a day in the 2 weeks leading up to admission and an additional 50 tablets just before presentation — for a recent “depressive episode”. Depression had not been formally diagnosed, and the tablets had been obtained “over the counter” from a local pharmacy.

A provisional diagnosis of seizures due to an overdose of SJW was made. High performance liquid chromatography was not performed to quantify hypericum extract in serum and urine, as these tests are not available in our hospital. A repeat EEG at discharge on Day 6 was normal, and there were no further seizures in the following 6 months. Psychiatric assessment during the patient’s hospital stay revealed a likely suicide attempt following recent social stresses.

There is some evidence for the efficacy of SJW in treating depression.1 In the United States and Australia it is available without prescription, but in Germany, where it is prescribed more frequently than fluoxetine for depression, it is available by prescription only.

The reported incidence of adverse drug reactions to SJW is 0–5.7%.2 Although these are usually minor and transient, more serious adverse reactions (such as serotonin syndrome) have been reported.3 SJW was implicated as a likely, but unproven, cause of seizure-related events in a recent review,4 but our case appears to be the most severe reported so far. Adverse reactions are thought to be more common if SJW is taken in conjunction with selective serotonin reuptake inhibitors, but have also been described when SJW is taken alone.5