Octreotide (OCT), a synthetic octapeptide analogue of nature somatostatin hormone has been extensively used in cancer treatment and growth hormone related diseases. Herein, a first efficient voltammetrical approach is presented for determination of OCT based on its strong hydrophobic interaction with the untreated carbon paste electrode (CPE) surface. The electrode reaction mechanism of OCT was proposed for the first time based on the presence of well-shaped irreversible and adsorption-driven oxidation peak of its Tryptophan amino acid moiety. The adsorption data is fitted well to Freundlich isotherm model indicating favorable and a physical multilayer adsorption process. Further, LS-AdASV and SW-AdASV methodologies involve the selection of optimal conditions for OCT oxidation at CPE, analytical performance and interference study. The usefulness of our elaborated electroanalytical protocolwas verified in the simple, sensitive and fast analysis of OCT in human plasma and its commercial formulation "Sandostatin injection". It also rendered low detection limit (LOD) of 7.66 x 10(-10) M in human plasma sufficient for clinical applications using SW-AdASV method. This direct electrochemical analysis of OCT molecule opens up new prospects for the detection of other peptides, hormones or proteins in biological samples and for development of various electrochemical sensor and biosensor devices for medicine and biochemistry. (c) 2019 The Electrochemical Society.