Haloperidol is a typical butyrophenone type antipsychotic that exhibits high affinity dopamine D 2 receptor antagonism and slow receptor dissociation kinetics.  It has effects similar to the phenothiazines .  The drug binds preferentially to D 2 and α 1 receptors at low dose (ED 50 = and mg/kg, respectively), and 5-HT 2 receptors at a higher dose (ED 50 = mg/kg). Given that antagonism of D 2 receptors is more beneficial on the positive symptoms of schizophrenia and antagonism of 5-HT 2 receptors on the negative symptoms, this characteristic underlies haloperidol's greater effect on delusions, hallucinations and other manifestations of psychosis.  Haloperidol's negligible affinity for histamine H 1 receptors and muscarinic M 1 acetylcholine receptors yields an antipsychotic with a lower incidence of sedation, weight gain, and orthostatic hypotension though having higher rates of treatment emergent extrapyramidal symptoms .
Unintentional overdose of an opioid can usually be managed expectantly; however, if partial reversal is necessary, very low-dose naloxone (formerly Narcan) can be quickly administered by giving - to -mg (or mcg per kg) intravenous or intramuscular boluses every three to five minutes, titrated to respiratory rate or mental status (mix one mg per mL ampule of naloxone with saline to make 10 mL, which equals mg per mL). 27 Continued close monitoring is necessary because duration of opioid effect may outlast naloxone.