Methiodone (IC-26, WIN 1161-3) is a synthetic opioid analgesic and methadone analogue developed by Sterling Drug Inc. In human studies, low oral doses frequently produced no clear subjective effects, while higher doses induced morphine-like effects with significant inter-individual variability. Twenty-four-hour substitution studies demonstrated that IC-26 effectively suppressed morphine withdrawal, and its addiction liability was concluded to be comparable to morphine.