a. Haloperidol alters the effects of and blocks receptors for the hormone dopamine within the central nervous system while also exhibiting anticholinergic ("drying out") and alpha-adrenergic blocking (lowering blood pressure) properties. Understanding of lorazepam's mechanism of action is still incomplete however, it is believed to cause central nervous system depression by potentiating the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) causing a hyperpolarization to occur resulting in lowered excitability.
b. IM administration of haloperidol has a listed onset of action between 20-30 minutes and IM administration of lorazepam has an onset of action between 30-60 minutes.
c. It is not recommended to administer sedative medications with antipsychotic medications because of their ability to cause profound sedation, however in an emergency situation, that may be the intended outcome. If a patient is aggressive, irritated, or agitated, possibly hostile and combative, these medications can chemically restrain the patient by producing a sedation level that calms them down, if not places them in a brief sleep, that allows the providers to provide the patient the care they require without risking their own wellbeing to do so. Example: if a patient is deliriously punching and kicking HCWs, giving these medications can ethically subdue the patient so the HCWs can perform the tasks needed.