Abstract Introduction Causes of medicines shortages are multifactorial. In February 2019, the Human Medicines Regulations 2012 introduced Serious Shortage Protocols (SSPs) to address medicines shortages. SSPs are issued by the Department of Health and Social Care and enable pharmacists to supply alternative medicines without amended prescriptions1. Aim This review aimed to explore contemporary reasons attributed to medicines shortages in the United Kingdom (UK) and analyse expired SSP records. Methods A rapid scoping literature review was conducted using National Library of Medicine (PubMed®) and Elsevier (ScienceDirect). Grey literatures were collated from the Pharmaceutical Journal, Google, and Public Health England’s grey literature index. Searches were limited to publications written in English, published since 2014, which met the inclusion criteria (medicines OR drugs AND shortages AND causes). Data extraction and analysis was performed using Microsoft Excel. Expired SSPs were extracted to Microsoft Excel and analysed using descriptive and inferential statistics on R software (v.4.3.2). SSP data is publicly available; therefore, no ethical approval was required. Results Causes of Medication Shortages A total of 11 papers were selected, in which 77 medicines shortage causes were discussed. Narrative analysis identified 10 shortage-drivers. The most frequent were Manufacturing and Quality Challenges (30%,23/77), Business and Commercial Issues (21%,16/77), and Regulatory Changes and Challenges (10%,8/77). Content analysis found that supply-driven issues were more frequently cited than demand-driven issues. SSP Analysis Between October 2019 and June 2024, 59 SSPs had expired2. Menopausal Hormonal Treatments (MHTs) were the most common medication class in shortage (41%,24/59), followed by antibiotics (17%,10/59), and antidepressants (12%,7/59). The mean shortage length was 129.2 days (IQR=51–196), the longest lasting 359 days (oestradiol 0.5mg/1mg gel sachets). Oestradiol transdermal medications accounted for 19 of 24 MHT SSPs. The mean MHT shortage length was 152.6 days (IQR=51.0–216.0). Phenoxymethylpenicillin accounted for 8 of 10 antibiotic shortages. All 8 phenoxymethylpenicillin SSPs were active from 15 December 2022 to 12 May 2023; 7 of 8 were oral solution formulations. The mean antibiotic shortage length was 168.8 days, which is significantly longer than the whole sample average (p<0.05, IQR=147.0–148.0). All antidepressant SSPs were fluoxetine capsules. The mean shortage length was 99 days (IQR= 35.5–122.0). Discussion Existing literature suggests supply-driven rather than demand-driven causes of medication shortages are more pertinent; however, most expired SSPs were issued in response to demand-driven factors, such as disease outbreaks and changing prescribing demand. This suggests the extent of demand-driven shortages is not reflected in current literature. Future research should explore how demand-driven causes of shortages can be mitigated. As a rapid scoping review was conducted, the full breadth of literature may not be presented. Additionally, the grey literature findings are limited by potential inaccuracies. Finally, the use of narrative analysis may limit the generalisability of identified shortage drivers. As of 05 June 2024, there are 5 active SSPs. With medicines shortages becoming normalised within the UK health system3, there is an urgent need to mitigate supply- and demand-driven causes. Additionally, further research should explore why certain medication classes are more frequently in shortage than others.