Anorexia is experienced by most people with lung cancer during the course of their disease and treatment. Anorexia reduces response to chemotherapy and the ability of patients to cope with, and complete their treatment leading to greater morbidity, poorer prognosis and outcomes. Despite the significant importance of cancer-related anorexia, current therapies are limited, have marginal benefits and unwarranted side effects. In this multi-site, randomised, double blind, placebo controlled, phase II trial, participants will be randomly assigned (1:1) to receive once-daily oral dosing of 100mg of anamorelin HCl or matched placebo for 12 weeks. Participants can then opt into an extension phase to receive blinded intervention for another 12 weeks (weeks 13–24) at the same dose and frequency. Adults (≥18 years) with small cell lung cancer (SCLC); newly diagnosed with planned systemic therapy OR with first recurrence of disease following a documented disease-free interval ≥6 months, AND with anorexia (i.e., ≤ 37 points on the 12-item Functional Assessment of Anorexia Cachexia Treatment (FAACT A/CS) scale) will be invited to participate. Primary outcomes are safety, desirability and feasibility outcomes related to participant recruitment, adherence to interventions, and completion of study tools to inform the design of a robust Phase III effectiveness trial. Secondary outcomes are the effects of study interventions on body weight and composition, functional status, nutritional intake, biochemistry, fatigue, harms, survival and quality of life. Primary and secondary efficacy analysis will be conducted at 12 weeks. Additional exploratory efficacy and safety analyses will also be conducted at 24 weeks to collect data over longer treatment duration. The feasibility of economic evaluations in Phase III trial will be assessed, including the indicative costs and benefits of anamorelin for SCLC to the healthcare system and society, the choice of methods for data collection and the future evaluation design.Trial registration.The trial has been registered with the Australian New Zealand Clinical Trials Registry [ACTRN12622000129785] and approved by the South Western Sydney Local Health District Human Research Ethics Committee [2021/ETH11339].https://clin.larvol.com/trial-detail/ACTRN12622000129785.