Polyethylene glycol 3350 (sold as MiraLAX and store-brand equivalents) is the only constipation treatment that received a strong recommendation for ongoing use from both the American Gastroenterological Association and the American College of Gastroenterology. In a six-month clinical trial, 43% of people taking it daily had consistent relief, compared to just 11% on placebo. But “best” depends on what’s causing your constipation, how quickly you need relief, and whether you’ve tried other options first. Here’s how the main categories compare.
Osmotic Laxatives: The First Choice
Osmotic laxatives work by drawing water into your intestines, which softens stool and makes it easier to pass. Polyethylene glycol 3350 is the standout in this category. It’s available without a prescription, works gently enough for daily use, and has the strongest clinical evidence behind it. You mix a measured dose of powder into a glass of water or another beverage once a day. Most people notice results within one to three days of starting, though the full effect builds over the first week.
Magnesium citrate is another osmotic option, but it works much faster and more aggressively. It typically produces a bowel movement within 30 minutes to 6 hours. That makes it useful for occasional, short-term relief when you need quick results, but it’s not a good choice for everyday use. Milk of magnesia (magnesium hydroxide) falls somewhere in between: gentler than magnesium citrate but faster-acting than polyethylene glycol. Both magnesium-based options can cause cramping and loose stools, and overuse carries a risk of electrolyte imbalances, particularly in older adults or people with kidney problems.
Lactulose is a prescription osmotic laxative that your doctor might suggest if over-the-counter options aren’t working. It’s effective but tends to cause more gas and bloating than polyethylene glycol because gut bacteria ferment it in the colon.
Fiber Supplements: Effective but Often Misunderstood
Not all fiber supplements are equal, and choosing the wrong one can actually make constipation worse. The key distinction is between fibers that hold water in your stool and fibers that don’t.
Psyllium husk (sold as Metamucil and generics) is the most effective fiber supplement for constipation. It forms a gel in your gut that holds onto water even as stool moves through the colon, keeping things soft. A dose of 3.5 grams twice a day is enough to see results. In a head-to-head trial against docusate (a popular stool softener), psyllium significantly increased stool water content within three days, while docusate had no measurable effect at all.
Wheat dextrin and inulin, two other common fiber supplements, can actually be counterproductive. Bacteria in your colon ferment them quickly, which destroys their water-holding ability and produces gas. Wheat dextrin can even have a constipating effect at typical doses of 10 to 15 grams per day. Insoluble fiber supplements (like wheat bran) work by mechanically stimulating your intestinal lining, which can help some people but may irritate others, especially those with irritable bowel syndrome.
Whichever fiber supplement you try, start with a low dose and increase gradually over a week or two. Drink plenty of water alongside it. Jumping to a full dose on day one is the most common reason people abandon fiber due to bloating and gas.
Stimulant Laxatives: For Short-Term or Rescue Use
Stimulant laxatives like bisacodyl (Dulcolax) and senna (Senokot) cause your intestinal muscles to contract, physically pushing stool along. They work fast, usually within 6 to 12 hours, which makes them a good option when you need reliable, quick relief.
Clinical guidelines give bisacodyl a strong recommendation for short-term use (under four weeks) or as “rescue therapy” when gentler methods aren’t enough on a given day. Many people who take a daily osmotic laxative keep a stimulant laxative on hand for the occasional tough stretch. The main downsides are cramping and the potential for dependency if used daily over long periods. Your intestines can start relying on the stimulation, which makes the underlying problem harder to manage.
Stool Softeners: Surprisingly Ineffective
Docusate sodium (Colace) is one of the most commonly recommended stool softeners, frequently suggested after surgery or alongside pain medications. The evidence, however, is damning. A comprehensive review of seven randomized, placebo-controlled trials published between 1956 and 2021 found that docusate at doses of 100 to 400 mg per day was no better than a sugar pill at softening stool. It had no significant effect on stool water content in any study.
If you’re currently taking docusate and it seems to be working, the placebo effect is likely doing the heavy lifting. Switching to psyllium or polyethylene glycol would give you actual pharmacological benefit. Despite the evidence, docusate remains widely stocked in hospitals and recommended by some providers out of long-standing habit.
Prescription Options When OTC Fails
If you’ve given an osmotic laxative like polyethylene glycol a genuine month-long trial at adequate doses and still aren’t getting relief, prescription medications are the next step. Guidelines from the VA and gastroenterology societies specifically require that patients try OTC osmotic laxatives first before moving to prescription therapies.
Prescription options for chronic constipation and constipation-predominant irritable bowel syndrome work by increasing fluid secretion into your intestines through a different mechanism than osmotic laxatives. They’re taken as daily capsules and tend to produce results within the first week. The most common side effects are diarrhea and, for some formulations, nausea. These medications are more expensive and require ongoing prescriptions, which is why they’re reserved for people who genuinely haven’t responded to over-the-counter treatments.
Constipation in Children
Polyethylene glycol is also the go-to treatment for children, dosed by weight: typically 0.4 to 0.8 grams per kilogram of body weight per day, dissolved in water. For more stubborn cases or initial “clean-out” phases, doctors may temporarily increase the dose to 1 to 1.5 grams per kilogram per day for three to six days.
Mineral oil is sometimes used in children as a lubricant laxative, but it should never be given to infants under one year old or to children with neurological impairments because of the risk of aspiration into the lungs. Sodium phosphate enemas are off-limits for children under two. For most kids with garden-variety constipation, increasing water and fiber intake alongside a short course of polyethylene glycol resolves things within a week.
Matching the Right Option to Your Situation
If your constipation is occasional and you want quick relief, magnesium citrate or a stimulant laxative like bisacodyl will get things moving within hours. If constipation is a recurring problem, polyethylene glycol taken daily is the best-supported long-term solution. Adding psyllium fiber can complement an osmotic laxative nicely, addressing both the water content and bulk of your stool.
Skip docusate entirely. Don’t rely on stimulant laxatives daily for more than a few weeks without medical guidance. And if you’re experiencing unexplained weight loss, blood in your stool, persistent abdominal pain, or fever alongside constipation, those symptoms point to something beyond simple constipation that needs evaluation.