The aim of the present study was to identify the efficacy and safety of Oncoxin-Viusid (OV) as a supportive treatment for patients with prostate cancer (PCA). A prospective, non-randomised, open-label phase II clinical trial, including 25 patients with hormone-refractory PCA (HRPC) was conducted at the Hospital Universitario General Calixto García (Havana, Cuba) between June 2017 and March 2018. Each of the patients received chemotherapy (CTX) and/or radiotherapy (RT) and OV treatment. Patients had a mean age of 73 years, clinical stage IV cancer and a high risk of relapse. Six cycles of CTX were completed by 80% of the patients, adverse reactions decreased and no weight loss was observed. Among the 25 patients, 5 were lost to follow-up and 4 died of disease progression. A total of 16 of these patients survived, of which 15 had an improved quality of life and 10 responded to treatment, with a significant reduction in pain and prostate symptoms and ≥50% reduction in baseline PSA. The progression-free survival (PFS) rate was 59% and the overall survival (OS) rate 64% at 1 year after treatment began. The OV nutritional supplement was effective, leading to a significant improvement in the patients' quality of life, good nutritional status and greater treatment tolerance. A clinical and humoral response was observed, with high survival rates and a delayed appearance of signs of disease progression. The present study was registered in ClinicalTrials.gov PRS with ID #NCT03543670.