Patients who are undergoing colonoscopy and are not adequately sedated after initial standard sedation with midazolam 5 mg and fentanyl 100 mcg will be randomly assigned to receive diphenhydramine vs. continued midazolam, and their level of sedation will be assessed. Our hypothesis is that diphenhydramine will provide better sedation than continued administration of midazolam during colonoscopy in patients not achieving adequate sedation with standard doses of midazolam plus fentanyl.

Patients who are undergoing colonoscopy and are not adequately sedated after initial standard sedation with midazolam 5 mg and fentanyl 100 mcg will be randomly assigned to receive diphenhydramine (up to 3 incremental doses of 25 mcg each) vs. continued midazolam (up to 3 incremental doses of 1.5 mg each). the level of sedation will be assessed using the MOAA/S scale 2-3 minutes after each administration to determine if they are sufficiently sedated to begin colonoscopy. The patient, the healthcare team involved in performing the endoscopy, and the investigator assessing sedation will be blinded to the therapy. Our hypothesis is that diphenhydramine will provide better sedation than continued administration of midazolam during colonoscopy in patients not achieving adequate sedation with standard doses of midazolam plus fentanyl.

Inclusion Criteria:

• Patients >18 years-old who are undergoing elective colonoscopy with conscious sedation

Exclusion Criteria:

• allergy or prior adverse reactions to diphenhydramine
• medical contraindications to use of diphenhydramine (e.g. closed angle glaucoma)
• pregnancy