Multiple drugs are used to provide anaesthesia. On average, four to six drugs are used during anaesthesia and, therefore, drug interactions are common. These interactions are primarily either pharmacokinetic or pharmacodynamic. Due to the relatively short duration of drug administration for anaesthesia, pharmacokinetic drug interactions resulting from alterations in drug metabolism do not generally produce clinically significant effects. Pharmacodynamic-drug interactions between anaesthetic drugs, however, are potentially serious. This may reflect that anaesthesia is not a single entity, but a process provided by a combination of drugs; i.e. loss of consciousness, analgesia and neuromuscular blockade. An understanding of each drug's pharmacokinetics, pharmacodynamics and drug interactions will allow clinicians to administer drugs to provide a more optimal anaesthetic.