AimsTo examine the patterns of use of potentially interacting supplement–drug pairs in adults with type 2 diabetes (T2D) in real-world settings, and to explore the impact of potentially interacting supplement–drug pairs on downstream outcomes. MethodsPotentially interacting supplement–drug pairs were identified from four tertiary databases. We categorized the potential pharmacodynamic interactions into different clinical types according to their related outcomes and explored their associations with incident outcomes using Cox models. Results26,394 participants with T2D in the UK Biobank were included. Half (48.5 %) were supplement users, of whom 85.0 % were taking potentially interacting supplement–drug pairs. The potential pharmacodynamic interactions were related to various clinical outcomes, including reducing the effects of glucose-lowering drugs (50.7 %), hypotension (49.8 %), bleeding (50.4 %) and hepatotoxicity (34.8 %). Exploratory analyses found that the use of potentially interacting supplement–drug pairs was associated with incident hepatic diseases (hazard ratio = 1.26, 95 % confidence interval 1.10–1.44, P < 0.001). ConclusionsReal-world data suggests that most adults with T2D who concurrently used supplements and drugs were on potentially interacting supplement-drug combinations, with the potential of causing adverse outcomes such as incident hepatic diseases. Clinicians should communicate with patients and assess the potential risk of supplement–drug interactions in clinical settings.