Samidorphan (INN, USAN) (developmental code names ALKS-33, RDC-0313), is an opioid antagonist which in the form of olanzapine/samidorphan (brand name Lybalvi) is used in the treatment of schizophrenia and bipolar disorder. Samidorphan reduces the weight gain associated with olanzapine. Samidorphan is taken by mouth.