The standard adult dose of MiraLax is 17 grams of powder once a day, which is exactly one capful filled to the white line inside the cap. You mix it into 4 to 8 ounces of any beverage (cold, hot, or room temperature), stir until dissolved, and drink it. That single daily capful is the over-the-counter dose for occasional constipation, and you should not use it for more than 7 consecutive days without a doctor’s guidance.
How to Measure the Right Dose
The MiraLax bottle cap doubles as your measuring tool. Fill the cap to the top of the white section, which is pre-marked to hold exactly 17 grams. If you’re using single-dose packets instead of the bottle, each packet contains 17 grams, so you use one full packet per dose. Either way, the amount is the same.
You can dissolve it in water, coffee, tea, juice, or any other beverage. There’s no taste or grit once it fully dissolves. Taking it at the same time each day helps keep things consistent, but there’s no strict requirement for morning versus evening dosing.
How Long It Takes to Work
MiraLax works by pulling water into the colon to soften stool and stimulate a bowel movement. It can take up to 24 hours to produce results, so don’t assume it isn’t working and take a second dose the same day. Some people notice effects within 12 hours, but the full day window is normal. This slower onset is what makes it gentler than stimulant laxatives, which force the intestinal muscles to contract.
The 7-Day Limit
The FDA-approved label is clear: do not use MiraLax for more than 7 days. If your constipation hasn’t resolved within a week, that’s a signal something else may be going on, whether it’s a medication side effect, a dietary issue, or an underlying condition that needs evaluation. Many doctors do prescribe MiraLax for longer-term use in chronic constipation, but that’s a decision made with monitoring, not something to do on your own with the over-the-counter product.
Colonoscopy Prep Is a Completely Different Dose
If your doctor has told you to use MiraLax as a bowel preparation before a colonoscopy, the dose is dramatically higher than the daily constipation dose. A typical colonoscopy prep calls for an entire 8.3-ounce bottle (238 grams) mixed into 64 ounces of a sports drink, consumed over several hours the day before the procedure. That’s roughly 14 times the standard daily dose. This is only done under a doctor’s specific instructions and is not something you should attempt for regular constipation.
Dosing for Children
MiraLax’s over-the-counter label is approved for adults and children 17 and older. For younger children, pediatricians sometimes recommend it off-label, but the dose depends on the child’s weight and the situation. Children’s Hospital of Philadelphia, for example, uses a weight-based dosing chart for bowel cleanouts that ranges from about 3 capfuls for a 22-pound child up to 11 capfuls for a child around 95 pounds, but these are medically supervised prep doses, not daily maintenance amounts.
For everyday childhood constipation, pediatricians typically prescribe a fraction of the adult capful based on the child’s weight. Never give a child MiraLax without checking with their doctor first, because children are more vulnerable to dehydration and electrolyte imbalances from laxative use than adults are.
What Happens If You Take Too Much
Taking more than the recommended 17 grams per day increases the risk of diarrhea, nausea, abdominal cramping, and vomiting. The bigger concern with excessive use is dehydration and electrolyte imbalance, particularly the loss of minerals like sodium and potassium that your body needs to function properly. These effects are more dangerous in children and older adults. If you’ve been doubling or tripling doses because one capful doesn’t seem to work, stop and talk to a doctor rather than escalating on your own.
People Who Need Extra Caution
MiraLax works locally in the gut and has very little absorption into the bloodstream, which is part of why it’s considered relatively safe. However, people with kidney disease need to be careful. The standard 17-gram dose of plain MiraLax (without added electrolytes) is used in kidney disease patients under medical supervision, but formulations that contain electrolytes can cause dangerous imbalances in people whose kidneys can’t clear those minerals efficiently. If you have kidney problems, confirm with your doctor which product is safe for you.
For pregnancy and breastfeeding, MiraLax is generally considered compatible. Its negligible absorption means very little, if any, passes into breast milk. The NHS Specialist Pharmacy Service notes that its high molecular weight limits both transfer into milk and absorption by the infant. As a precaution, monitoring the infant for diarrhea or irritability is reasonable.
Signs Your Constipation Needs Medical Attention
MiraLax is designed for occasional, uncomplicated constipation. Certain symptoms point to something that a laxative won’t fix. Watch for bleeding from the rectum or blood on toilet tissue, black or unusually colored stools, stomach pain that doesn’t go away, unexplained weight loss, or constipation symptoms lasting longer than three weeks. Any of these warrant a visit to your doctor rather than continued self-treatment.