Excellent question. It is very important that your son not use marijuana before any type of procedure, especially procedures involving sedation. Marijuana is in part a sedative, so using it in combination with powerful sedatives such as Propofol places him at risk of serious complications. Additionally, preps before colonoscopies can dehydrate patients, which marijuana also does, particularly in the upper airway where the endoscope will pass for the procedure, placing him at increased risk of perforation. I recommend your son stop smoking marijuana entirely for many reasons, but especially so before a major procedure. I hope this helps. Dr. Sheppe