Medicinal chemistry is strongly focused on discovering new antitumor agents that are both more effective and less toxic. Thiosemicarbazones and their metal complexes have demonstrated properties suitable for a variety of applications, making these molecules attractive for further evaluation as potential new therapeutic agents in cancer treatment. The administration of new heterocyclic Schiff bases and their copper complexes with thiosemicarbazones exerts varied influences on lipid peroxidation indices in the supernatant. The general objective of this study was to investigate the effects of nine copper coordination compounds with thiosemicarbazones (CCT) and doxorubicin, compared to controls, on lipid peroxidation markers via an in vitro experiment. A series of in vitro experiments was performed on peripheral blood samples collected from 10 apparently healthy individuals. All samples were tested in duplicate. The results showed that, depending on their chemical structure and concentration, these compounds exert a selective action on lipid peroxidation markers. In this study, changes in advanced protein oxidation products and reactive oxygen metabolites were statistically inconclusive with regard to lipid peroxidation processes, as the prooxidant–antioxidant balance became more pronounced in order to reduce reactive oxygen and nitrogen species. The influence of the studied preparations on lipid peroxidation demonstrated differing effects on malondialdehyde (MDA) levels: at a concentration of 10 μM/L, a prooxidant increase was observed, whereas at 1 μM/L, MDA levels decreased, indicating enhanced antioxidant activity.