Serlopitant, Originally developed by Merck, is a once-daily oral NK1 receptor antagonist being developed for the treatment of pruritus, or itch, associated with various conditions such as prurigo nodularis, psoriasis and chronic pruritus of unknown origin. It is highly selective for the human NK1 receptor and in both animal and human testing it has been well tolerated. In 2012, Merck licensed serlopitant to Menlo to develop it in indications other than nausea and vomiting. Development of serlopitant for the treatment of overactive bladder, alcohol dependence and pruritus was discontinued at phase II, by Merck & Co. and Japan. Menlo has completed three positive Phase 2 clinical trials with serlopitant showing a statistically significant reduction in pruritus compared to placebo. Serlopitant has been evaluated in over 1,600 patients and has been shown to be well-tolerated, including in patients who have received treatment for up to one year. Serlopitant is an investigational drug that is not currently approved for use in any indication in any country.