RNA editing is a post-transcriptional process, which has the potential to alter the function of encoded proteins. In particular, serotonin 2C receptor (5-HT2cR) mRNA editing can produce 24 protein isoforms of varying functionality. Rodent studies have shown that 5-HT2cR editing is dynamically modulated in response to environmental challenges. Basal extracellular serotonin, which is strongly influenced by serotonin transporter (SERT), was proposed as a potential trigger for this modulation; however, the data remain inconclusive. Here, 5-HT2cR editing is evaluated in SERT mutant versus wild-type rats, and in humans with different SERT genotypes. Our findings argue against the hypothesis that 5-HT2cR editing efficiency is regulated by extracellular serotonin levels.