A thorough drug history is necessary to establish what medication the patient is taking both prescribed and bought at a pharmacy and over the counter (OTC) at supermarkets and local stores. In some cases, drugs may be obtained from friends and relatives. You need to know this for a number of reasons not least because it may be that the medication the patient is taking is the cause of the patient’s presenting problem(s) or there may be side effects contributing.

An important consideration is to always include the possibility of an adverse drug reaction in your differential diagnosis (see Adverse Drug Reactions). It might be that the patient has had their presenting problem previously diagnosed and is not taking a prescribed drug treatment correctly or perhaps has not taken it at all. Enquiring whether the patient is taking prescribed medication as intended by the prescriber links well into determining whether the patient understands why the medication was prescribed in the first place and therefore is the medication still necessary?

Current medication may preclude the use of other medications due to a potential interaction between the two. (See Drug Interactions) If you are clerking a patient for an inpatient stay in hospital clearly their regular medications will need to continue. Whether the patient is sensitive or allergic to any medication is crucial so that you do not inadvertently prescribe that treatment. In patients who give a history of allergy to a drug, establishing the history of the allergy and trying to ascertain whether the patient has a ‘true’ allergy is necessary as your first line treatment options are narrowed if there are drugs that you cannot prescribe due to allergy. (See also Adverse Drug Reactions). The patient’s past medical history (PMH) is important with reference to medication history as often patients can forget the drugs they take but will remember their medical conditions and if prompted can link it to a medication.