Diphenhydramine as an adjunct to sedation for colonoscopy: a double-blind randomized, placebo-controlled study

Gastrointest Endosc. 2006 Jan;63(1):87-94. doi: 10.1016/j.gie.2005.08.015.


Background: Intravenous benzodiazepines in combination with opiates are used to achieve moderate sedation for colonoscopy. Although effective, these agents have potential adverse effects, such as respiratory depression and hypotension. Diphenhydramine hydrochloride possesses central nervous system depressant effects that theoretically could provide a synergistic effect for sedating patients.

Objective: The objective was to assess the efficacy of adding diphenhydramine hydrochloride as an adjunct to improve sedation and to reduce the amount of standard sedatives used during colonoscopy.

Design: We conducted a prospective, randomized, double-blind, placebo-controlled study.

Setting: The study was conducted in a university hospital with an active GI fellowship training program.

Patients: The study group comprised 270 patients undergoing screening/diagnostic/therapeutic colonoscopy were enrolled.

Interventions: Patients were randomized to receive either 50 mg of diphenhydramine or placebo, given intravenously 3 minutes before starting conscious sedation with intravenous midazolam and meperidine.

Main outcome measurements: The main outcome measure was anesthetic effect as assessed by the endoscopy team and by the patient; quantity of adjunctive sedatives to achieve adequate sedation.

Results: Of 270 patients, data were analyzed for 258 patients, with 130 patients in the diphenhydramine group and 128 patients in the placebo group. There was a 10.1% reduction in meperidine usage and 13.7% reduction in midazolam usage in favor of the diphenhydramine group. The mean evaluation scores as judged by the faculty, the fellows, and the nurses were statistically significant in favor of the diphenhydramine group. In addition, patient scores for overall sedation and pain level favored the group that received diphenhydramine.

Conclusions: Intravenous diphenhydramine given before initiation of standard sedation offers a significant benefit to conscious sedation for patients undergoing colonoscopy.

Publication types

  • Randomized Controlled Trial

MeSH terms

  • Colonoscopy*
  • Conscious Sedation / economics
  • Conscious Sedation / methods*
  • Diphenhydramine* / economics
  • Double-Blind Method
  • Female
  • Humans
  • Hypnotics and Sedatives* / economics
  • Male
  • Meperidine / administration & dosage
  • Midazolam / administration & dosage
  • Middle Aged
  • Patient Satisfaction
  • Prospective Studies
  • Treatment Outcome


  • Hypnotics and Sedatives
  • Diphenhydramine
  • Meperidine
  • Midazolam