Most people start having bowel movements within one to three hours after taking their first Sutab tablets, and the frequent trips to the bathroom typically last about three to four hours per dose. Since Sutab is taken in two separate doses (a split-dose prep), you should expect two distinct rounds of bathroom activity spread across the evening before and the morning of your colonoscopy.
When Bowel Movements Start
After swallowing the 12 tablets of your first dose with water, your body needs time to absorb the salts and pull fluid into your intestines. Most people feel the first urge to go within one to two hours, though it can take up to three hours for some. The process starts gradually, often with mild cramping or a rumbling sensation, and then picks up quickly.
Once things get going, expect frequent, urgent trips to the bathroom. Early bowel movements look like loose stool, but they rapidly transition to watery diarrhea. This intense phase usually lasts two to four hours after each dose. The second dose follows the same pattern, sometimes moving a bit faster because your colon is already mostly cleared out.
The Two-Dose Timeline
Sutab uses a split-dose schedule, meaning you take 12 tablets the evening before your colonoscopy and another 12 tablets closer to the procedure. A typical timeline looks like this:
- Dose 1 (around 4 p.m. the day before): You swallow the tablets with 16 ounces of water over 15 to 20 minutes, then drink two more 16-ounce containers of water over the next hour and a half. Bowel movements usually begin within one to two hours and taper off by late evening.
- Dose 2 (evening before or morning of): The timing depends on your scheduled arrival. For morning procedures, many centers have you start dose 2 around 11 p.m. the night before. For afternoon procedures, you might start as late as 8 or 9 a.m. the day of. Expect another round of bathroom trips lasting two to three hours.
Memorial Sloan Kettering’s prep instructions lay out the dose 2 timing by appointment time. If you’re scheduled to arrive at noon, for example, you’d start dose 2 at 5 a.m. For a 2 p.m. arrival, you’d start at 7 a.m. The idea is to finish your bowel movements well before you need to leave for the procedure.
What Your Stool Should Look Like
The goal is to produce colorless or near-colorless liquid by the time you’re done. Early on, you’ll pass solid or semi-solid stool, which quickly turns to brown and then yellow or green watery diarrhea. Yellow and green are completely normal and don’t mean something is wrong. You’re looking for the liquid to become light yellow to clear, similar to urine or light broth. That’s the sign your colon is clean enough for the doctor to get a good view during the colonoscopy.
If your output is still dark brown or has solid pieces after finishing both doses, your prep may not be complete. This is worth calling your doctor’s office about before you head in for the procedure.
How Sutab Works in Your Body
Sutab tablets contain sulfate salts that your intestines can’t easily absorb. When these salts sit in your gut, they pull large amounts of water from your body into your intestinal tract through osmosis. That flood of water loosens and flushes everything out. This is why drinking the required water is so critical to the process: you’re providing the raw material your body uses to clean the colon, and replacing what you’re losing.
Each dose requires you to drink a total of 48 ounces of water in three separate 16-ounce rounds, spaced out over roughly two hours. On top of that, you should be sipping clear liquids throughout the day. The Cleveland Clinic recommends at least 12 servings of 8 to 10 ounces of clear liquids in addition to the water taken with the tablets. Dehydration is the biggest practical risk, so keep drinking even if you feel full or nauseated.
Side Effects During the Prep
Nausea is the most common complaint. In clinical trials involving nearly 1,000 patients, about half reported nausea during the prep. Bloating affected roughly 30% of people, and somewhere between 16% and 23% experienced vomiting. These side effects are usually worst during or shortly after swallowing the tablets and tend to ease once the bowel movements begin.
Stomach cramping is also common and tends to come in waves, peaking right before a bowel movement. Staying near the bathroom, wearing comfortable clothing, and using wet wipes or a barrier cream can make the experience significantly more tolerable. The skin around the anus gets irritated quickly from the repeated wiping, so applying petroleum jelly or a zinc oxide cream before you start can help.
Tips for Getting Through It
Chill the water. Room temperature water with Sutab tablets often triggers more nausea than cold water. You can also suck on hard candies (nothing red or purple) between water rounds to settle your stomach and break up the monotony of drinking so much liquid.
Plan to stay home from the moment you take your first dose. You won’t want to be in a car or anywhere without immediate bathroom access. Set up camp near your bathroom with your phone, a book, or something to watch. Most people find the first dose is the harder one because there’s more material to clear. The second dose moves through faster and tends to feel less intense, though the urgency can still catch you off guard.
If you’re taking the second dose in the early morning hours, set an alarm with plenty of buffer time. You need to finish drinking all the required water, then allow two to three hours for the bowel movements to taper off before leaving for your appointment. Rushing this process or skipping water to “get it over with” leads to a poorly prepped colon, which can mean a repeat colonoscopy sooner than necessary.