Auditory evoked potentials (AEPs) provide a correlate of cognitive dysfunction in schizophrenia. Both cognitive dysfunction and AEP characteristics might be related to reduced glutamatergic neurotransmission as induced by glutamate-antagonist-like ketamine. Hypericum perforatum (St John’s wort) extract has demonstrated a ketamine antagonising effect. German researchers examined whether such an extract reverses changes of a low-dose ketamine on AEPs in healthy subjects. They performed a double-blind randomised treatment with either 2 × 750 mg extract or placebo given for 1 week, using a crossover design, in 16 healthy subjects. A test battery, including AEPs, the oculodynamic test (ODT) and a cognitive test, was performed before and after an infusion with 4 mg of S-ketamine over a period of 1 h. S-ketamine led to a significant decrease in the N100-P200 peak-to-peak (ptp) amplitude after the placebo treatment, whereas ptp was significantly increased by S-ketamine infusion in the extract-treated subjects. The ODT and the cognitive testing revealed no significant effect of ketamine infusion and therefore no interaction between treatment groups.