Using supermarket loyalty card data to investigate seasonal variation in laxative purchases in the UK

While laxatives are designed to manage the symptoms of constipation, they are also frequently misused for weight control, particularly by individuals with eating disorders. This study aims to investigate the relationship between laxative purchases and weight management by examining seasonal trends in laxative purchasing. Using real-world transaction data from a major UK pharmacy retailer spanning December 2013 to December 2014, we analyse purchasing patterns from 748,375 buyers to explore potential links with weight control behaviours. In pre-registered analysis, we use regression models to investigate our hypotheses: that the number of doses purchased would be greater in January compared to the previous December (reflecting motivations in relation to "New Years resolutions" around weight loss), and greater in May-August compared to the subsequent September (reflecting an increased focus on body image during the summer). We examine differences between stimulant and non-stimulant laxatives, as stimulants are more commonly misused for weight control due to their rapid effects. To validate our findings, we compare purchasing patterns with those for diet and weight management products over the same periods, and also include negative controls of unrelated medication groups (i.e., painkillers, cold and flu, and hay fever medications). Our findings reveal seasonal variations in laxative purchasing, particularly for non-stimulant medications. Purchases increase in January compared to December and are higher in some summer months compared to September, suggesting potential use for weight control. Non-stimulants exhibit greater seasonal fluctuation than stimulants. Purchase of weight management products followed similar patterns, aligning with established seasonal trends in weight loss behaviours. Laxative purchases show seasonal trends aligned with other weight management produce purchases, potentially aligned to use motivated by body image concerns. These findings provide retrospective support for the MHRA stimulant laxative policy change and highlight the need for further evaluation of its impact. Author SummaryLaxatives are commonly used to relieve constipation, but they can also be misused by people trying to lose weight--particularly those struggling with eating disorders. We wanted to understand whether people in the UK might be using laxatives for weight control at certain times of the year. To do this, we analysed loyalty card data from a large UK pharmacy to look at when people bought laxatives over a one-year period. We found that purchases of laxatives increased during the summer months, a time when many people focus on their appearance and may try to lose weight because of the warmer weather. We also saw similar patterns in purchases of diet-related products, which supports the idea that laxatives may sometimes be used for weight management. Our research shows how loyalty card data can offer insights into health behaviours in the general population. These findings could help inform public health efforts and policy, especially around eating disorders and the regulation of over-the-counter medications. This approach could also be applied to other types of health-related behaviours, offering a new way to support early identification and intervention.