Drug overdose is often caused by combining two or more depressant drugs, although overdose is also possible by consuming a large dose of one depressant drug. Central nervous system depression can also be caused by the accidental or intentional inhalation or ingestion of certain volatile chemicals such as butanone (contained in plastic cement) or isopropyl alcohol. Other causes of central nervous system depression are metabolic disturbances such as hypoglycaemia.[4]