Introduction: This article discusses agomelatine (Valdoxan ™/Thymanax ™; Servier/Novartis), which is a melatonin (MT1/MT2) agonist and serotonin (5-HT2c) receptor antagonist. Agomelatine has been approved for the treatment of adults with major depression by several regulatory agencies and is now on the market in 41 countries. Areas covered: Literature related to agomelatine was reviewed on PubMed using the search terms 'agomelatine OR S-20098' and 204 articles were found. Twelve published, randomized, double-blind studies were included in this review. Expert opinion: Agomelatine produces strong effects on circadian sleep phase disturbances, improving time to sleep onset and quality of sleep. It has been shown to be superior to placebo and similar to existing antidepressants, as demonstrated by short-term clinical trials and one relapse prevention trial. However, 0 0.6% and 3 4.5% of patients treated with 25 and 50 mg, respectively, showed elevated transaminases. Although none of these reactions so far seem to have been serious, the adverse effects in the liver may present a regulatory and marketing challenge. Given equivalence or modest superiority to existing, generic alternatives, the acceptability in a third-party reimbursement environment is questionable. Future clinical trials are needed to establish an appropriate market niche. © 2011 Informa UK, Ltd.