Colace and Miralax are not the same medication. They contain different active ingredients, work through different mechanisms, and belong to different drug categories. Colace (docusate sodium) is a stool softener, while Miralax (polyethylene glycol 3350) is an osmotic laxative. Both are used to treat constipation, but they go about it in distinct ways.
How Each One Works
Colace acts like a detergent inside your intestines. It lowers the surface tension between oil and water in your stool, which lets more water and fats soak into the stool mass. The result is softer stool that moves through the intestinal tract more easily. It doesn’t stimulate your bowels to contract or push things along; it simply changes the consistency of what’s already there.
Miralax takes a different approach. Its active ingredient forms hydrogen bonds with water molecules inside your gut, preventing your intestines from reabsorbing that water back into the body. This keeps extra water in the stool and increases osmotic pressure in the intestinal lumen. That additional water softens stool and triggers more frequent bowel movements. Your body barely absorbs Miralax itself, so it passes through the digestive system doing its work almost entirely locally.
How They Compare in Effectiveness
A multicenter study of 180 hospitalized pediatric patients compared docusate and PEG 3350 head-to-head. Within 72 hours, 66.7% of patients on docusate had a bowel movement compared to 71.1% on PEG 3350. The average time to first bowel movement was 48.9 hours for docusate and 45.4 hours for PEG 3350. Neither difference was statistically significant, making this the first study to show comparable efficacy between the two in pediatric patients.
In adults, the evidence picture is less balanced. A joint clinical practice guideline from the American Gastroenterological Association and the American College of Gastroenterology noted a “paucity of data” for docusate when it comes to chronic constipation. The guideline didn’t even issue a formal recommendation for it. Miralax, by contrast, has a stronger evidence base for chronic use and is more commonly recommended in clinical guidelines for ongoing constipation.
Onset and Dosing
Both medications take roughly the same amount of time to work. With Colace, you can expect a bowel movement within 12 to 72 hours, though it may take one to three days to notice real improvement. Miralax also produces a bowel movement in one to three days.
The standard adult dose of Colace is 100 mg twice per day, taken as a capsule. Miralax comes as a powder you dissolve in a beverage, with a standard adult dose of 17 grams once per day. Many people find the powder easier to take since it’s tasteless and odorless, though the pediatric study mentioned above found similar rates of dose refusal for both medications (around 40%).
Side Effects
Both medications are generally well tolerated. The most common side effects for either one are mild digestive symptoms like bloating, gas, or cramping. In the head-to-head pediatric study, loose stools occurred at the same rate in both groups (3.3%). Diarrhea was somewhat more common with Miralax (15.6%) than with Colace (6.7%), though that difference didn’t quite reach statistical significance. This makes intuitive sense: Miralax draws more water into the bowel, so overshooting the mark is more likely.
Safety During Pregnancy
Both Colace and Miralax are considered safe during pregnancy. Docusate sodium has been studied in pregnant women without evidence of adverse effects. There is one isolated case report linking chronic docusate use throughout pregnancy to low magnesium levels in the newborn, but this hasn’t been replicated. Miralax is poorly absorbed into the bloodstream, so systemic exposure to the fetus is minimal. That said, osmotic laxatives like Miralax are generally recommended for short-term or occasional use during pregnancy to avoid dehydration or electrolyte shifts.
Can You Take Both Together?
There are no known drug interactions between Colace and Miralax, and they don’t trigger therapeutic duplication warnings since they belong to different drug classes. Some people do use both simultaneously, pairing the stool-softening action of Colace with the water-retaining effect of Miralax for more stubborn constipation. Because they work through completely separate mechanisms, combining them can make sense when one alone isn’t enough.
Which One to Choose
Colace is often recommended for situations where you want to prevent straining, such as after surgery, during pregnancy, or when you have hemorrhoids. It’s a gentler intervention that simply makes stool easier to pass. Miralax is typically the go-to for more persistent or chronic constipation, backed by stronger clinical guideline support for long-term use. If your constipation is occasional and mild, either one is a reasonable starting point. For constipation that doesn’t respond to a stool softener alone, Miralax is the more evidence-supported step up.