The indiscriminate or continuous use of any drug without medical supervision is dangerous. Even drugs considered harmless may result in chronic poisoning if used for a period of years. Pharmacists should not renew prescriptions without consulting the doctor. The doctor prescribed a given amount because he or she wished to limit use of the drug to a certain time. Never use a drug prescribed for someone else just because your symptoms appear similar. There may be differences, apparent to an expert but hidden from you, that indicate an entirely different ailment requiring different medication.The passage best supports the statement that