1. EXECUTIVE SUMMARY1.1. BACKGROUNDThe UK National Health Service (NHS) faces the triple challenge of improving health outcomes while coping with the increasing demand for services and achieving efficiency savings. Medicines optimisation can improve health outcomes and reduce costs. However, addressing suboptimal use of medicines in an effective and cost-effective manner requires an understanding of the size and nature of the evidence base. The objectives of this work are, firstly, to undertake a scoping review relating to the suboptimal use of medicines in the NHS, both in terms of the scale, costs and health lost; and, secondly, to review the extent of the evidence on effectiveness and cost-effectiveness of interventions to address suboptimal use of medicines.1.2. METHODSSystematic searches (up to February 2013) of the NHS Economic Evaluation Database, the Cochrane Database of Systematic Reviews and the Database of Abstracts of Reviews of Effects are undertaken to identify for systematic reviews on the effectiveness or cost-effectiveness and for primary research on cost-effectiveness of interventions. Studies in English set in any country are included. Suboptimal use of medicines is categorised in a number of different aspects on discussions with advisors and a brief review of the area: compliance with guidelines, inappropriate prescribing, prescriptions errors, medicines reconciliation and discharge, dispensing errors, administration errors, medicines management in care homes, adherence and monitoring errors.1.3. RESULTSIn total, 107 studies are included in the review (29 economic evaluations and 78 systematic reviews) from 646 records identified.Systematic reviews on effectiveness of interventionsWith the exception of insufficient prescribing of low cost generics and record keeping, every one of the aspects of suboptimal medicines use is addressed by the systematic reviews. The majority of the studies (51, 65%) focussed on interventions to improve adherence, either in any disease area (21; 27%) or in specific conditions (30, 38%). Randomised controlled trials (RCTs) are available for all aspects. There is considerable evidence on the different aspects of suboptimal medicines use specific to the UK setting. Most studies report intermediate outcomes: measures of adherence (53, 68%), clinical outcomes (24, 31%) and adverse drug events (16, 21%). No study reports quality-adjusted life years but four (5%) report measures of quality of life.Economic evalu...