Merfadon was a type of sedative. In 2373, Silaran Prin used merfadon to sedate Kira Nerys with the intention of removing the unborn Kirayoshi O'Brien, so that no innocents would die when he murdered her for disfiguring him. However, the makara herbs Kira took for her pregnancy counteracted the drug, allowing her to deceive and subdue Prin. (DS9: "The Darkness and the Light")