Many types of new drugs have been developed in accordance with numerous advances in medicine. New drugs may be more effective than old ones, but they may sometimes provoke serious adverse reactions. Medical professionals should make efforts to acquire current knowledge via medical articles, conferences and by other means. Instructions on drug label are also important materials for doctors to prescribe drugs, and play significant roles in finding medical faults. They contain the highest level of information provided by pharmaceutical companies. When doctors prescribe medicine or pharmacists fill the prescription, the instructions must be noted first. Therefore, prescriptions of drugs contrary to the instructions on the drug label may lead to doubts about whether the doctor is at fault. In actual medical practice, doctors commonly prescribe drugs for off-label use. Off-label use can be defined as the practice of prescribing drugs for an unapproved indication or in an unapproved age group, at an unapproved dose or in an unapproved form of administration. Although the off-label use of prescription drugs involves unpredictable risks, it may be necessary to treat some cases of diseases. In these cases, a higher duty of care is required compared to cases of the approved use of drugs. Especially where there are alterative approved medications, all of the information about off-label drug prescriptions has to be provided so that patients can decide upon their treatment. Doctors must let patients compare the benefits and risks of off-label use and must advise them to choose their own therapy. Patients have the right of self-determination, whereas doctors have the obligation to provide information to patients. This information has the role of not only in raising patients' autonomy but also helping patients appropriately manage the adverse effects of off-label drug use. As drug information alerts patients to possible adverse effects, they can detect even subtle changes in their own body early after taking the drugs. Doctors have to instruct patients to cope with the adverse effects of drugs should they arise. Health care problems, such as outbreaks of antimicrobial resistant organisms and the rapid increase in health care expenditures, must be taken into account when doctors prescribe medicine. Therefore, legal policies for health care can be considered with the presumption of medical errors.