Background: There is a growing number of service users looking to discontinue use of psychiatric medicines. Tapering is the recommended approach for reducing and/or discontinuing the use of psychiatric medicines. This involves gradually reducing the dose over time to minimise the potential for withdrawal symptoms. However, many uncertainties exist regarding the process of reducing and stopping psychiatric medicines. This study will use a James Lind Alliance Priority Setting Partnership to determine the Top 10 unanswered questions and uncertainties about reducing and stopping psychiatric medicines. Methods: The Priority Setting Partnership will be conducted using the James Lind Alliance methodology. It will involve seven stages: (i) creating an international Steering Group of representatives from key stakeholder groups that will include people with lived experience of taking and/or stopping psychiatric medicines, family members, carers/supporters and healthcare professionals, and identifying potential partners to support key activities (e.g. dissemination); (ii) gathering uncertainties about reducing and stopping psychiatric medicines from key stakeholders using an online survey; (iii) data processing and summarising the survey responses; (iv) checking the summary questions against existing evidence and verifying uncertainties; (v) shortlisting the questions using a second online survey; (vi) determining the Top 10 research questions through an online prioritisation workshop; (vii) disseminating results. Conclusions: This study will use a Priority Setting Partnership to generate a Top 10 list of research questions and uncertainties about reducing and stopping psychiatric medicines. This list will help to guide future research and deliver responsive and strategic allocation of research resources, with a view to ultimately improving the future health and well-being of individuals who are taking psychiatric medicines.