Experimental studies to test interventions for people living with HIV in low- and middle-income countries are essential to ensure appropriate and effective clinical care. The implications of study participation on outcome data in such populations have been discussed theoretically, but rarely empirically examined. We aimed to explore the effects of participating in a randomised controlled trial conducted in an HIV clinic in Mombasa, Kenya. We report qualitative data from the Treatment Outcomes in Palliative Care trial, which evaluated the impact of a nurse-led palliative care intervention for HIV positive adults on antiretroviral therapy compared to standard care. Participants in both arms attended five monthly quantitative data collection appointments. Post-trial exit, 10 control and 20 intervention patients participated in semi-structured qualitative interviews, analysed using thematic analysis. We found benefit attributed to the compassion of the research team, social support, communication, completion of patient reported outcome measures (PROMs) and material support (transport reimbursement). Being treated with compassion and receiving social support enabled participants to build positive relationships with the research team, which improved mental health and well-being. Open and non-judgmental communication made participants feel accepted. Participants described how repeated completion of the PROMs was a prompt for reflection, through which they began to help themselves and self-care. Participant reimbursements relieved financial hardship and enabled them to fulfil their social responsibilities, enhancing self-worth. These findings emphasise the importance of compassion, support and effective communication in the clinical encounter, particularly in stigmatised and isolated populations, and the potential of the integration of simple PROMs to improve patient outcomes. Participation in research has unexpected positive benefits for participants, which should be taken into account when designing research in similar populations. Researchers should be aware of the effects of financial reimbursement and contact with researchers in isolated and impoverished communities.