The investigators believe that glucagon therapy will have a positive impact on key parameters of colonoscopy such as cecal intubation time, withdrawal time, total procedure time, adenoma detection rate, endoscopist's assessment of the difficulty of the procedure, patient comfort, and patient's willingness to undergo a repeat colonoscopy.

Glucagon transiently decreases peristalsis of smooth muscle in the gastrointestinal tract. It is widely used by radiologists to improve diagnostic yields of upper and lower GI barium contrast examinations. Glucagon is also routinely administered intravenously for all endoscopic retrograde cholangiopancreatography (ERCP) throughout the United States to facilitate canulation of the duodenal papilla and sphincterotomy. Glucagon has been used at the dose of 1-3 mg intravenously by Dr. John Cello in over 5000 ERCP examinations. The role of glucagon in facilitating colonoscopy remains controversial however and is not considered "routine". Several studies have evaluated the effect of glucagon on colonoscopy with varying results. No large scale randomized controlled trial has been performed to conclusively establish the effect of routine glucagon administration prior to colonoscopy. The investigators plan to carry out a randomized double blind, placebo controlled trial that studies key parameters of a colonoscopy such as cecal intubation time, withdrawal time, total procedure time, adenoma detection rate, endoscopist's assessment of the difficulty of the procedure, patient comfort, and patient's willingness to undergo a repeat colonoscopy.

Inclusion Criteria:

• Any subject who has already been already cleared for and scheduled to undergo colonoscopy at SFGH endoscopy center.

Exclusion Criteria:

1. Refusal to give informed consent.
2. Age <18 or >70.
3. Prior intra-abdominal surgery
4. Diabetes
5. Pheochromocytoma
6. Insulinoma
7. Liver disease (Child-Pugh Score >6)
8. Pregnancy

During colonoscopy procedure (an average of 1139 seconds for Glucagon Arm and 1353 seconds for Placebo Arm)