Intravenous injection of self-produced ephedrone (metcathinone) using potassium permanganate as an oxidant can lead to severe, fixed encephalopathy. This risk applies mainly to young individuals experimenting with “home-made” drugs and results in an irreversible aggravation of overall functioning. Besides multiple neurological symptoms and movement disorders, affected individuals also experience cognitive dysfunction. No systematic research has been conducted in this field. Single case reports and small group descriptions show that assessment with screening tools such as the Mini-Mental State Examination (MMSE) is ineffective. Neuropsychological assessment conducted with other tests indicates significant dysarthric speech disorders, psychomotor function impairment, attentional disorders of varying intensity as well as dysfunctions of verbal and visual working memory processes. Some studies of this group of subjects also indicate working memory and executive function disorders. These dysfunctions seem to be permanent and do not recede following manganese use discontinuation and an improvement of the neuroradiological picture in MRI assessment. A standard test battery should be developed enabling the assessment of both cognitive and neurological dysfunctions that otherwise render some tests impossible to administer.