B52 (medical treatment)
A B52 is a single intramuscular injection used to calm someone who is very agitated. It contains three medicines: diphenhydramine (Benadryl), haloperidol (Haldol), and lorazepam (Ativan). The letters stand for Benadryl, 5 for 5 mg of haloperidol, and 2 for 2 mg of lorazepam.
Haloperidol helps by blocking dopamine in the brain, which can reduce agitation. Lorazepam helps relax and sedate by boosting the brain’s GABA system. Diphenhydramine is included to provide additional sedation and to reduce movement problems from haloperidol, but evidence for its extra benefit is not strong.
A 2021 review questioned the routine use of diphenhydramine, noting good evidence for haloperidol and lorazepam but not for diphenhydramine. A 2022 retrospective study suggested against including diphenhydramine, finding it linked to longer emergency department stays, lower oxygen levels, and more use of restraints, with a lower risk of movement side effects.
This page was last edited on 3 February 2026, at 03:33 (CET).