The best thing to buy for constipation depends on how quickly you need relief. For same-day results, a stimulant laxative like senna or bisacodyl works within 6 to 12 hours. For a gentler approach that takes a couple of days, an osmotic laxative like polyethylene glycol 3350 (MiraLAX) or a fiber supplement like psyllium (Metamucil) is a better fit. Here’s a breakdown of every major category on the pharmacy shelf so you can pick what matches your situation.
Fiber Supplements for Mild or Recurring Constipation
If your constipation is mild or keeps coming back, a bulk-forming fiber supplement is the gentlest starting point. These products absorb water in your intestines, making stool larger and softer so it moves through more easily. The most common options are psyllium (sold as Metamucil or Konsyl), methylcellulose (Citrucel), and calcium polycarbophil (FiberCon).
Psyllium powder is typically taken at about 3.4 grams mixed into a full glass of water, one to three times a day. Methylcellulose powder runs about 2 grams per dose, also one to three times daily. Calcium polycarbophil starts at 1 gram once daily and can be increased to four times a day if needed. All three are also available as capsules or caplets if you dislike the texture of powder mixed in liquid.
The trade-off with fiber supplements is patience. You can expect a bowel movement within 12 to 72 hours, and it can take two to three days to feel the full effect. Drinking plenty of water alongside them is essential, because without enough fluid they can actually make things worse. These products are well suited for people who want a daily maintenance approach rather than a one-time fix.
Osmotic Laxatives for Reliable, Moderate Relief
Osmotic laxatives work by pulling water into the colon, which softens stool and stimulates your intestines to move things along. Polyethylene glycol 3350, sold as MiraLAX and several store brands, is the most widely recommended option in this category. You dissolve one capful in any beverage once daily. It typically produces a bowel movement within two to four days, making it slower than stimulant options but very well tolerated with minimal cramping.
Magnesium hydroxide, better known as Milk of Magnesia, is another osmotic option that tends to work faster, often within 30 minutes to 6 hours. It’s a reasonable choice when you want something stronger than fiber but aren’t ready for a stimulant laxative. One thing to keep in mind: people with kidney problems should avoid magnesium-based laxatives, since the kidneys are responsible for clearing excess magnesium from the body.
Stimulant Laxatives for Faster Results
When you need a bowel movement relatively soon, stimulant laxatives are the strongest oral option on the shelf. Senna (Senokot) and bisacodyl (Dulcolax) both trigger contractions in the intestinal muscles, physically pushing stool forward. Oral doses of either one produce results in roughly 6 to 12 hours, so many people take a dose at bedtime and have a bowel movement the next morning.
The downside is that stimulant laxatives can cause abdominal cramps and pain because of those intestinal contractions. They’re best used for short-term, occasional relief rather than daily use. If you find yourself reaching for senna or bisacodyl more than a couple of times a week, a fiber supplement or osmotic laxative taken regularly is a better long-term strategy.
Stool Softeners: Gentle but Limited
Docusate sodium (Colace) is the most common stool softener. It works by allowing water and fat to penetrate the stool, making it softer and easier to pass. It’s often recommended after surgery or during pregnancy because it’s very gentle.
How effective is it on its own? A clinical trial comparing docusate to polyethylene glycol 3350 found no significant difference between the two. About 67% of patients on docusate had a bowel movement within 72 hours, compared to 71% on polyethylene glycol, and the average time to the first bowel movement was similar (roughly 49 hours versus 45 hours). So docusate does work, but it’s not dramatically faster or more effective than an osmotic laxative. It’s a reasonable choice if your stool is hard and dry and you want something mild, but it won’t help much if the core problem is that things simply aren’t moving.
Suppositories and Enemas for Same-Day Relief
If you need relief within the hour, rectal products are the fastest option. Glycerin suppositories work by drawing water into the rectum and lubricating the stool. You insert one, wait 15 to 60 minutes, and the urge to go typically follows. If nothing happens within an hour, that’s a sign to contact a healthcare provider rather than insert another one.
Saline enemas (like Fleet) work on a similar principle but introduce liquid directly into the lower colon, producing results in 2 to 15 minutes for most people. Both options bypass the entire digestive tract and act locally, which means they’re useful when oral laxatives haven’t worked or when you’re dealing with a stubborn blockage near the exit point. They’re not meant for regular use, but they’re effective tools when you’re genuinely uncomfortable and need fast relief.
Food-Based Options Worth Trying First
Before heading to the pharmacy, prunes and prune juice are worth a shot. Prunes contain sorbitol, a natural sugar alcohol that draws water into the intestines the same way an osmotic laxative does. They also provide fiber and contain compounds that stimulate intestinal contractions. A reasonable starting dose for adults is four to eight ounces of prune juice daily, or about six whole prunes.
Other foods that help include kiwifruit (two per day has solid evidence behind it), ground flaxseed mixed into yogurt or oatmeal, and high-fiber foods like beans, lentils, and whole grains. Increasing water intake alongside fiber-rich foods makes a noticeable difference. These approaches work best for mild constipation or as a complement to an OTC product.
What About Probiotics?
Probiotics are marketed heavily for digestive health, and there is some evidence they can help with constipation. Strains in the Bifidobacterium family appear to be the most promising. However, the evidence is still inconsistent. The studies done so far have been small, used different strains and doses, and produced widely variable results. There’s currently no specific strain, dose, or duration that experts can confidently recommend for constipation. A probiotic supplement is unlikely to hurt, but it shouldn’t be your primary strategy if you’re actively uncomfortable.
Choosing Based on Your Situation
Here’s a practical way to think about your options:
- Occasional mild constipation: Start with prunes, extra water, and high-fiber foods. If that’s not enough, add a psyllium or methylcellulose supplement.
- Constipation lasting several days: Polyethylene glycol 3350 (MiraLAX) or Milk of Magnesia will get things moving within a day or two.
- Need relief tonight or tomorrow morning: Senna or bisacodyl taken at bedtime works within 6 to 12 hours.
- Need relief right now: A glycerin suppository or saline enema provides the fastest results.
- Hard, dry stools without urgency: Docusate sodium (Colace) softens stool over one to three days.
Safe Options During Pregnancy
Constipation is extremely common during pregnancy, and many OTC products are considered safe. The University of Colorado Anschutz Medical School lists Metamucil (psyllium), FiberCon (calcium polycarbophil), Colace (docusate sodium), plain Senokot (senna), and Milk of Magnesia as appropriate options during pregnancy. Starting with fiber and a stool softener is the most conservative approach before moving to stronger options.
Red Flags That Need More Than OTC Products
Most constipation responds well to something from the pharmacy shelf. But certain symptoms signal that you need a medical evaluation rather than another laxative. Blood in your stool, severe abdominal pain, unexplained weight loss, or constipation lasting longer than three weeks all warrant a visit to your doctor. These can indicate something beyond simple functional constipation that OTC products won’t address.