Naltrexone is an organic heteropentacyclic compound that is naloxone substituted in which the allyl group attached to the nitrogen is replaced by a cyclopropylmethyl group. A mu-opioid receptor antagonist, it is used to treat alcohol dependence. It has a role as a mu-opioid receptor antagonist, a central nervous system depressant, an environmental contaminant, a xenobiotic and an antidote to opioid poisoning. It is an organic heteropentacyclic compound, a morphinane-like compound and a member of cyclopropanes. It is a conjugate base of a naltrexone(1+).