Background Advanced cancer patients often experience multiple symptoms at a same time. This might lead to polypharmacy and increase adverse events representing major threats to the quality of health care, especially in palliative care situations. Mirtazapine, an antidepressant agent, has been suggested as a potential relevant drug to alleviate multiple cancer-related symptoms at a same time. Therefore, the present study aims to assess the effectiveness of mirtazapine in alleviating multiple symptoms at a same time in advanced cancer patients suffering from a major depressive episode compared to a group receiving escitalopram, another antidepressant agent. Methods Multicentre, prospective, randomized, controlled trial in 12 palliative care services in France. The study will be based on a mixed-method methodology using parallel groups, of oral mirtazapine compared with oral escitalopram, with a 56 day follow-up. The primary outcome will be an improvement of the Global health Status (issued from the EORTC-QLQ-C30) on day 56. 418 participants will be clinically followed-up on day 7 and 56 and will have a telephonic assessment on days 14 and 28. A sub-sample of participants will be invited to take part in semi-structured qualitative interviews at baseline and day 56. For the qualitative part, purposeful sampling will be used. Discussion This study will provide evidence for the pharmaceutics management of poly-symptomatology in advanced cancer patients. This could lead to important changes in the management of those patients by using a single molecule to alleviate multiple symptoms at a same time, potentially improving medication adherence, symptoms’ control, and reducing the risk of medications adverse events. Trial registration Trial registration: NCT04763135 . Registered 18 March 2021.