Methadone (Met) mainly acts as a μ-opioid receptor agonist. Recent evidence pointing towards the role of Met in sensitization of certain cancer cell lines to chemotherapeutic agents has promoted the hypothesis that Met may be a useful adjuvant to cancer chemotherapy. We wanted to address whether Met has, alone or in combination with a chemotherapeutic agent, an effect on melanoma cell viability in vitro. Only a small fraction (4.3%) of our 102 melanoma biobank cell lines with RNA sequencing data showed expression of the main receptor for Met (OPRM1). We assessed the viability of melanoma cell lines with high, medium or low/no OPRM1 expression (OPRM1 , OPRM1 , OPRM1 ) 72 hours after treatment with Met alone or combined with cisplatin (Cis). Our analyses show that Met alone did not affect cell viability. While Cis/Met treatment did not have an effect on viability of OPRM1 or OPRM1 cell lines, it resulted in a slightly decreased cell viability of OPRM1 cells. Clinically, concurrent temozolomide/Met treatment did not have an effect in our single-case report of a patient suffering from uveal melanoma. Taken together, our findings do not provide evidence for recommending Met as an adjuvant to chemotherapy in melanoma patients. This article is protected by copyright. All rights reserved.