Professional communication is essential in health care to ensure that all health care professionals who are caring for the same patient share the same information, and that any potential problems associated with their care are resolved. In relation to medication, this means that information on all medicines (both prescribed and over the counter) used by the patient should be available, including dosages, formulations, indications, contra-indications, and allergies. Correct information on medication is vital when prescribing new medications (in order to avoid duplication, contraindicated medication, or drug-drug interactions) and when diagnosing diseases (symptoms may be caused by adverse drug reactions [ADRs] rather than an underlying disease).