There are emerging concerns that loot boxes – digital video game items that can be purchased for a chance at randomised rewards – are associated with problematic gambling behaviours and, in turn, are potentially harmful. Current research suggests consistent correlations between loot box spending and problematic gambling symptomology, however little research has looked at relationships with mental wellbeing. Here, we used a Bayesian hypothesis testing framework to assess the relative strength of evidence for relationships between loot box spending, excessive gaming, problem gambling, mental wellbeing and psychological distress. 2,728 participants who reported playing games containing loot box mechanics in the past month answered a survey assessing the above measures, as well as other forms of digital spending. The results showed extremely strong evidence for a positive correlation between loot box spending and problem gambling; however there was no evidence to suggest relationships between such spending and mental wellbeing or psychological distress. Exploratory results suggested that individuals who spend money on loot boxes also spend more across a range of digital purchases generally. The findings highlight an urgent need to understand what constitutes harm when considering loot box spending effects, and provide further context for discussions regarding how best to regulate such mechanisms.