A Dulcolax suppository works by delivering bisacodyl directly into the rectum, where it stimulates the nerve endings in the intestinal wall to trigger strong, wave-like muscle contractions called peristalsis. These contractions push stool toward the exit, while the drug also prompts the colon to draw water into the bowel, softening the stool so it passes more easily. Because the active ingredient is absorbed right where it’s needed, a suppository typically produces a bowel movement within 15 to 60 minutes.
What Happens Inside the Colon
The suppository is made of bisacodyl suspended in a base of hydrogenated vegetable oil. Once inserted, your body heat melts the oily base, releasing bisacodyl against the rectal lining. The drug acts on two targets simultaneously. First, it stimulates sensory nerve endings embedded in the colon wall. These nerves are part of a network that controls gut movement, and when bisacodyl activates them, the muscles surrounding the colon begin contracting rhythmically to move contents forward.
Second, bisacodyl changes the way the colon handles water and salts. Normally, the colon absorbs water from stool as it passes through. Bisacodyl partially blocks this reabsorption and even causes the intestinal lining to secrete extra fluid into the bowel. The result is softer, bulkier stool that’s easier to pass, combined with stronger muscle contractions pushing it along. This dual action is why bisacodyl is classified as a “stimulant laxative” rather than a simple stool softener.
Why Suppositories Act Faster Than Tablets
Dulcolax also comes as an oral tablet, but the suppository works significantly faster. An oral bisacodyl tablet has an enteric coating that prevents it from dissolving until it reaches the small intestine, meaning the drug has to travel through most of the digestive tract before it arrives at the colon. That process takes roughly 6 to 12 hours, which is why oral tablets are often taken before bed for a morning result.
A suppository bypasses all of that. It delivers bisacodyl directly to the lower colon and rectum, so the drug begins working almost immediately on contact. Most people feel the urge to go within 15 to 60 minutes. This makes the suppository form particularly useful when you need faster relief or when swallowing a tablet isn’t practical.
How to Use It Correctly
Lie on your left side with your lower leg straight and your upper knee bent toward your chest. This position aligns the rectum for easier insertion. Gently push the suppository, pointed end first, about one inch past the opening. If it slides back out, it wasn’t inserted far enough. Try to hold it in for 15 to 20 minutes before allowing a bowel movement. The urge may come sooner, but giving the suppository time to fully dissolve improves results.
Drink plenty of water before and after use. Stimulant laxatives increase the amount of fluid the colon pulls from your body, so staying hydrated helps prevent cramping and dizziness. Aim for at least 8 ounces of water around the time you use the suppository, and continue drinking fluids throughout the day.
Common Side Effects
The most frequently reported side effects are stomach cramps, general abdominal discomfort, and a burning sensation in the rectum. The rectal burning tends to be mild and short-lived, fading once the suppository has fully dissolved and a bowel movement occurs. Some people also experience brief faintness, especially if they strain or if the laxative causes a sudden, large loss of fluid.
Rectal bleeding is less common but more serious. If you notice blood, stop using the suppository. Bleeding can signal irritation to the rectal lining or an underlying condition that needs evaluation.
How Long You Can Safely Use It
Bisacodyl suppositories are meant for short-term, occasional use. The NHS recommends not using bisacodyl every day for more than 5 days. If you’re still constipated after that window, the problem likely needs a different approach.
The reason for this limit is that your colon can become dependent on the stimulation. With prolonged daily use, the nerve endings in the bowel wall grow less responsive to normal signals, making it harder to have a bowel movement without the drug. Over time, this can damage the bowel, lead to chronic electrolyte imbalances (particularly low potassium and sodium), and even contribute to malnutrition because the colon isn’t absorbing nutrients properly. None of these risks apply to occasional use, but they build with repeated, daily reliance on any stimulant laxative.
Storing Suppositories
Because the suppository base is hydrogenated vegetable oil, it melts easily. Store them at room temperature between 59°F and 86°F (15°C to 30°C), and never exceed 86°F. A hot bathroom, a car glove box in summer, or a shelf near a stove can all soften or deform the suppository, making it harder to insert and potentially reducing how evenly it releases the active ingredient. If a suppository has partially melted and resolidified, it may not work as well. Refrigerating them briefly before use can make insertion easier, especially in warm climates.