How Long Does MiraLax Stay in Your Body Systems?

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How long does MiraLax stay in your systems (digestive systems and blood)?

According to clinical trials, MiraLax stays around three days in your digestive system after the last dose. Also, MiraLax is minimally absorbed into the blood. And it can be detected for about 18 hours after the last dose.

MiraLax is considered generally safe. The active ingredient (polyethylene glycol 3350) has a good safety profile across several studies.

MiraLax acts mainly inside your digestive system. And this makes MiraLax generally accepted and safe for the elderly, children, and pregnant women (reference).

Keep reading the next sections if you are concerned about the possible adverse events of the prolonged stay of MiraLax in your systems. 

Is the amount of MiraLax reaching your blood significant?

MiraLax acts mainly inside your digestive system. It is an osmotic laxative. It draws water to your colon to help to soften the stool.

It is considered more effective and more tolerable than other laxatives as lactulose. MiraLax produces fewer side effects than lactulose (such as bloating, colics, and nausea) (reference).


A small percentage of MiraLax is absorbed into the blood and excreted through the kidneys. The amount absorbed into the blood and then excreted into urine is only about 1/500 of the ingested dose or 0.2% (reference)

The average time MiraLax takes to be cleaned from your blood is about 18 hours after the last dose.

(The picture shows the trend of plasma concentration of MiraLax with time (hours)). (SOURCE)

But you should note the dose of MiraLax is minimal, and your body can eliminate it safely even with mild degrees of kidney impairment.

Polyethylene glycol 3350 (the active ingredient in MiraLax) has a good safety profile across studies.

Are higher doses of MiraLax take longer to be cleared?

MiraLax is famous for being taken in very large doses during colon preparation for colonoscopy.

The usual dose of MiraLax is 17 grams in 8 ounces of fluid once daily. During Colon Preparation, You may repeat the above dose every 10-15 minutes. This continues until 2 liters of fluid is consumed in one day.

Such a Megadose of MiraLax may raise the question about its safety. you may wonder if this large MiraLax dose takes longer to be cleared from your systems.

Unfortunately, we couldn’t find pharmacological studies evaluating the concentration and the time of clearance of MiraLax with such doses.

However, MiraLax mega doses during colon preparation are widely used and proven safe even in children (reference).

But some reports correlated polyethylene glycol used in children for a long period or larger doses To complications.

The FDA has received reports of complications such as metabolic acidosis and neurological and psychiatric complications in children (reference)

The neuro-psychiatric complications included fits, confusion, anxiety, and behavioral changes.

However, no confirmed causal relationship existed between MiraLax and such side effects. And the FDA concluded that no action is needed toward MiraLax.

Related: The Dose of Miralax for severe constipation.

Related: Can you take MiraLax 3 times a day?

Related: Does MiraLax work for stool impaction?

What are the possible adverse effects of MiraLax?

As we explained before, MiraLax is considered a safe medication. The majority of reported side effects are usually benign.

The adverse effects usually occur due to its presence inside your intestines and colon.

The most frequent system to be affected is the gastrointestinal tract.

The most commonly reported side effect is diarrhea (which is not bad if you have constipation).

Other side effects with their frequency are enlisted in the table below (reference).

MiraLax Adverse effects Frequency
Total gastrointestinal side effects 32%
Diarrhea 11%
Flatulence and Gas 7%
Nausea 6%
Abdominal pain 5%
Loose stool 4%
Abdominal distension and bloating 3%
Dyspepsia, eructation, stomach discomfort uncommon
Severe hypersensitivity reaction Rare


The above symptoms are expected to improve after Miralax is cleared from your digestive system.

The small percentage of MiraLax absorbed into your blood doesn’t seem to cause noticeable adverse effects.

So, Don’t worry about MiraLax reaching your circulation as long as you have normal renal function,

Nausea and vomiting are very common when using MiraLax for colonoscopy preparation. This is because your stomach and digestive tract less tolerate larger doses.

An extremely rare side effect, hypersensitivity to PEG solution, is also reported.

Conclusion: what you need to know.

  • Polyethylene glycol  3350 (MiraLax) is generally safe and well-tolerated Laxative.
  • No need to worry about trace amounts that stay in your digestive or other body systems.
  • MiraLax takes three days to be cleared from your digestive system.
  • MiraLax is minimally absorbed into your blood (only 0.2%).
  • MiraLax stays detectable for about 18 hours after the last dose.
  • The adverse effects of MiraLax staying longer in your body systems are usually minimal and tolerable.