Background Letters are regularly sent by healthcare organisations to healthcare professionals to encourage them to take action, change practice or implement guidance (e.g., regarding immunisation, blood pressure measurement, prescription, referral). However, whether letters are an effective tool in delivering a change in healthcare professional behaviour is currently uncertain. A systematic review was conducted to identify what information and behaviour change techniques (BCTs) within letters have the potential to optimise behaviour change in healthcare professionals.

Methods A comprehensive literature search of published and unpublished studies (grey literature) in five electronic databases (MEDLINE, Embase, PsycINFO, the Cochrane Library and CINAHL) was conducted to identify randomized controlled trials (RCTs) that met the inclusion criteria. Supplementary searches in Google Scholar, hand searches in relevant journals, and backward and forward citation searching of included studies and relevant reviews were also conducted. A systematic approach to searching, screening, reviewing and data extraction was applied in accordance with the process recommended by the Cochrane Collaboration. Two researchers examined titles, abstracts, full-texts for eligibility independently. Risk of bias (RoB) was assessed using Cochrane RoB for randomized controlled trials. In addition, intervention and comparator group material were coded by two independent reviewers into their BCTs using the BCT taxonomy version 1. Disagreements were resolved by a consensus procedure.

Results The search of the predefined databases resulted in 6004 records, while a further 1334 records were found from other sources, giving a total of 7,338 citations. After duplicates were removed (n = 3,241), a total of 4,097 citations were screened against the inclusion criteria. Of these, 4,012 citations were excluded on the basis of title, keywords, and abstract. The full texts of the remaining articles (n = 85) were then assessed against the inclusion criteria, resulting in 36 RCTs being retained. The studies were assessed as either low or unclear risk of bias. The majority of the RCTs investigated behaviour regarding antibiotic prescribing among physicians. The findings suggest that letters that incorporate social norms techniques are effective and can lead to behaviour change, with the potential for change in clinical outcomes. The effects might be enhanced by use of behavioural instruction, and a high-profile messenger.

Conclusion The evidence from this review provides important insights for healthcare providers and health authorities regarding how to formulate the communication, and what information and behaviour change techniques to include in order to optimise the potential effect on the behaviour of the receivers.