The authors report a 19-year-old woman who developed convulsions preceded by nasal ingestion of a cocaine mimic named 'the bubble' or mephedrone, obtained legally from a 'headshop' in Dublin. Characteristic posterior white matter oedema on brain imaging after the seizure suggested a diagnosis of posterior reversible encephalopathy syndrome (PRES). While PRES has been rarely associated with cocaine ingestion, this is the first report of an association with mephedrone.