Treatment of cancer often requires the use of adjuvant chemotherapy (ACT). In real clinical practice, numerous patients suffer from severe toxicity and reduced quality of life (QoL). Hence, there is a need to maintain QoL and to reduce therapy toxicity to comply with recommended chemotherapy (CT) regimens. The present study focused on the effects of the multi-component nutritional supplement Oncoxin (ONCX) on QoL and CT-induced toxicity in patients undergoing ACT. A total of 133 patients aged 50-70 years with gastric cancer IIB-IIIC or non-small cell lung cancer IIB-IIIA were enrolled in the present study: 84 received ONCX, and 49 were included in the control arm and received CT only. It was identified that after 2 weeks of treatment the patients receiving ONCX exhibited clinically meaningful improvement of QoL (measured by Edmonton Symptom Assessment System Questionnaire) compared with those in the control group (odds ratio, 2.07; 95% CI, 1.00-4.29). By the end of a 3 week-period, the albumin level was higher in patients of the ONCX group compared with those in the control group (mean, 38.1; 95% CI, 37.1-39.1 g/l; vs. mean, 35.5; 95% CI, 33.9-37.0; P=0.03; respectively). Furthermore, the use of ONCX substantively reduced the hepatic toxicity of ACT. The present prospective real clinical setting study revealed positive effects of ONCX on QoL and ACT toxicity. The present study was retrospectively registered under the study registration number NCT03550482 at ClinicalTrials. gov (June 8, 2018). © 2019 Spandidos Publications. All rights reserved.