The actual procedure takes about 30 minutes, but you have to prepare for it several days in advance. Follow your doctor's instructions.The doctor may give you a diet to follow several days prior to the test.You may have to stop taking certain dietary supplements several days before the test.Make sure the gastroenterologist knows all your prescription meds and follow instructions about your dosing schedule. Ask if you are uncertain.The day before the test you usually are on clear liquids only. Even blue and red colors might need to be avoided.The evening before the test, the doctor will have you take something to clean out your gut. It could be pills or you might drink a liquid. (tip: If it is a liquid mix, they don't necessarily taste good. Use a straw. Stay close to a bathroom.) You might be directed to use an enema.Usually, you cannot eat or drink anything within 2 hours of the test.You will need someone to drive you to and from the clinic.Follow instructions closely. You don't want to get this far then do something that will cancel the test.There are several different methods to prep for a colonoscopy and they have changed over the years.On the more humorous side: How long is a colonoscopy? About 5 feet.