Abstract Aim Medicines non-adherence is associated with poorer outcomes and higher costs. COVID-19 affected access to healthcare, with increased reliance on remote methods, including medicines supply. This study aimed to identify what affected people’s adherence to medicines for long-term conditions (LTCs) during the pandemic. Subject and methods Cross-sectional online survey of UK adults prescribed medicines for LTCs assessing self-reported medicines adherence, reasons for non-adherence (using the capability, opportunity and motivation model of behaviour [COM-B]), medicines access and COVID-19-related behaviours. Results The 1746 respondents reported a mean (SD) of 2.5 (1.9) LTCs, for which they were taking 2.4 (1.9) prescribed medicines, 525 (30.1%) reported using digital tools to support ordering or taking medicines and 22.6% reported medicines non-adherence. No access to at least one medicine was reported by 182 (10.4%) respondents; 1048 (60.0%) reported taking at least one non-prescription medicine as a substitute; 409 (23.4%) requested emergency supply from pharmacy for at least one medicine. Problems accessing medicines, being younger, male, in the highest socioeconomic group and working were linked to poorer adherence. Access problems were mostly directly or indirectly related to the COVID-19 pandemic. Respondents were generally lacking in capabilities and opportunities, but disruptions to habits (automatic motivation) was the major reason for non-adherence. Conclusion Navigating changes in how medicines were accessed, and disruption of habits during the COVID-19 pandemic, was associated with suboptimal adherence. People were resourceful in overcoming barriers to access. Solutions to support medicines-taking need to take account of the multiple ways that medicines are prescribed and supplied remotely.