6β-naltrexol

**6β-naltrexol** is a small molecule opioid receptor antagonist and the major active metabolite of naltrexone. It acts as a neutral antagonist at the μ-opioid receptor (MOR), with additional affinity for κ-opioid (KOR) and δ-opioid receptors (DOR). Unlike naltrexone—which is an inverse agonist—6β-naltrexol does not reduce basal MOR signaling and therefore has a lower risk of precipitating opioid withdrawal. It exhibits peripheral selectivity due to limited blood–brain barrier penetration but can antagonize central opioid effects at higher concentrations. In clinical studies it was effective in blocking morphine-induced gastrointestinal transit delay without affecting central analgesia or causing withdrawal symptoms. Its primary investigated indication was for opioid-induced constipation; however development for this use was not further pursued[1][7][9].

Other names

6β-hydroxynaltrexoneNaltrexone-6-beta-olNaltrexone6-beta-olNaltrexone 6-beta-ol3-(cyclopropylmethyl)-1,2,4,5,6,7,7a,13-octahydro-4,12-methanobenzouro[3,2-e]isoquinoline-4a,7,9-triol