sentences:  Prescription misuse has been defined differently and rather inconsistently based on status of drug prescription, the uses without a prescription, intentional use to achieve intoxicating effects, route of administration, co-ingestion with alcohol, and the presence or absence of dependence symptoms.Chronic use of certain substances leads to a change in the central nervous system known as a 'tolerance' to the medicine such that more of the substance is needed in order to produce desired effects.With some substances, stopping or reducing use can cause withdrawal symptoms to occur, but this is highly dependent on the specific substance in question.