Samidorphan-d5 (ALKS-33-d5) is is a deuterated compound of Samidorphan. Samidorphan is an orally active opioid system modulator that binds with high affinity to μ-opioid , κ-opioid , and δ-opioid receptors. Samidorphan is a μ-opioid receptor antagonist and a partial agonist at k-opioid and δ-opioid receptors. Samidorphan acts primarily as an opioid receptor antagonist in vivo.