Miralax Vs. Lactulose


Polyethylene glycol (Miralax) is an over-the-counter medication for treating constipation. Lactulose is an oral medication to help relieve the same condition. But in some cases, it can also relieve complicated liver problems. You can find Lactulose under the brand name "Generlac” and polyethylene glycol under the brand name “Miralax.”

Constipation does not always seem like a serious issue. But sometimes it is. It occurs when there are fewer bowel movements, and stools become difficult to pass. Sometimes it happens due to changes in routine or diet. Other times, it can be due to a low intake of FIBER. Constipation that lasts longer than three weeks can pose various complications.

Occasional constipation is common in people of all ages. But some people are more likely to deal with it than others. People more vulnerable to getting constipation include:

  • Older people (due to slower metabolism and less activity)
  • Women, especially after childbirth
  • People who do not eat enough fiber
  • Those who take certain medications
  • People with neurological and digestive disorders

About Miralax And Lactulose

What Is Miralax?

Miralax is an osmotic laxative. Osmotic laxatives work by drawing water into your stool. As a result, you have softer stools. Your bowel movements are also easier to pass. Healthcare professionals prescribe it for short-term use. In case of chronic constipation, let a doctor evaluate you first. They will decide the right course of treatment for you. They may even suggest long-term treatment with Miralax.

What Conditions Is Miralax Approved to Treat?

The FDA has only approved this drug for adults. This is because of a lack of clinical trials in children. The agency approved this drug in 1999. Miralax treats short-term constipation. In some cases, it also treats long-term constipation. After a careful evaluation, your doctor may also prescribe it for colonoscopy bowel preparation.

A colonoscopy exam helps your doctor examine your rectum and colon. It is an effective way to find out if one has colon cancer. Miralax causes bowel movement within 1 to 3 days of taking it. But this may not be the case for everyone.

How Does Miralax Work for Constipation?

Osmotic laxatives like Miralax have substances that don’t absorb well. They help draw water into the bowel lumen. Due to good water retention in the lumen, you experience loose stools. The mechanism of action focuses on unblocking the digestive system naturally. When there is more water in the lumen, it increases stool volume. It also stretches the wall of the bowel. Then, it triggers the defecation reflex.

Most people can easily tolerate this drug. But, as with everything else, Miralax can also trigger gastrointestinal side effects.

What Is Lactulose?

Lactulose first came into being in the 1920s. At the time, it was an effective way to treat constipation. Even today, it works for the same purpose. Lactulose is a synthetic sugar consisting of galactose and fructose.

What Conditions Is Lactulose Approved to Treat?

The FDA approved Lactulose in 1997. Apart from constipation, it also eases the symptoms of hepatic encephalopathy. Hepatic encephalopathy is a disorder of the nervous system. It is a result of severe liver disease. When the liver functions improperly, it gives rise to toxins in the blood. These toxins affect brain function. Chronic constipation, on the other hand, consists of the following:

  • Bloating
  • Hard and infrequent stools
  • Abdominal pain

How Does Lactulose Work for Constipation?

The colon breaks it down into different products. These products pull water into the colon. This water turns your stools soft. Lactulose also reduces the amount of ammonia in your blood. So, it works well for people with liver disease too. The drug helps draw ammonia from the blood into your colon. From here, your body actively removes it.


How Effective Are Miralax and Lactulose for Constipation?

A study evaluated the safety and efficacy of Miralax for occasional constipation. Participants consisted of patients over 17 years of age. They either received Miralax (PEG 3350 17 g) or a placebo. The treatment went on for a week. The efficacy variable was the resolution of hard stools and straining. The results concluded that oral administration of PEG 3350 was effective. Patients tolerated it well. Their occasional constipation also got better.

Lactulose, on the other hand, can take a few days to work. If you experience constipation even after three days, speak to your doctor.

A study compared lactulose syrup to a placebo in 66 volunteers. 42 were normal, and 24 had chronic constipation. In normal subjects, the dosage was 30 and 60ml per day. In subjects with constipation, the dosage was 60ml per day. Lactulose led to an increase in the frequency, volume, and weight of stools. It also led to an increase in the water content of stools. The drug produced softer stools. Even the adverse effects weren't severe. Researchers concluded that Lactulose is effective in inducing fecal evacuation.

Dosage Information

How Is Miralax Administered?

Miralax comes in powder form. You can mix it in water according to your doctor’s instructions. Here are more details about its dosage.

How Is Lactulose Administered for Constipation?

Lactulose comes in the following forms:

  • Oral powder
  • Oral solution
  • Rectal solution

Healthcare professionals suggest taking it orally for constipation. Here’s more information about its dosage.

Side Effects

Both Miralax and Lactulose carry their own side effects. If you experience the following, speak to your doctor immediately. You can also stop your medicine if they advise.

What Are the Most Common Side Effects of Lactulose?

The most common side effects of Lactulose include the following;

  • Decreased urine
  • Confusion
  • Dizziness
  • Fainting
  • Dry mouth
  • Irritability
  • Thirst
  • Irregular heartbeat
  • Lightheadedness
  • Irritability
  • Mood changes
  • Loss of appetite
  • Cramps and muscle pain
  • Vomiting
  • Nausea
  • Restlessness
  • Tingling or numbness in the lips, hands, or feet

Are There Any Potentially Serious Side Effects of Lactulose?

If you experience the following, consult a doctor immediately.

  • Trouble breathing
  • Seizures
  • Severe diarrhea
  • Unusual weakness
  • Stomach or intestinal cramps

What Are the Most Common Side Effects of Miralax?

The most common side effects of Miralax include the following;

  • Bloating
  • Stomach pain
  • Nausea
  • Gas
  • Loose stools or diarrhea

Are There Any Potentially Serious Side Effects of Miralax?

Serious side effects of Miralax include:

  • Unusual fatigue
  • Dry mouth
  • Confusion
  • Dizziness
  • Thirst
  • Irritability
  • No wet diapers for hours (in children)

Warnings and General Precautions for Miralax and Lactulose

There are various general precautions to observe when taking these medications. Before taking Miralax, inform your doctor if:

  • You are pregnant
  • You are breastfeeding

You also want to consult your doctor for the right dosage. Make sure not to continue taking it after two weeks. Again, this is a decision your healthcare provider should take for you. If you miss a dose, take it as soon as you can. If it’s time for the next dose, skip the last one. Do not take an extra dosage to make up for the missed one.

Before taking Lactulose, inform your doctor if:

  • You are diabetic
  • You already take other laxatives
  • There is an anti-infective drug you’re taking

Lactulose contains galactose and lactose, which may be harmful to diabetics. It's important to use the drug with caution if you're pregnant. There are no significant side effects, even if you use it during pregnancy. But there isn't enough research to establish its safety for pregnant women. Avoid overdosing on either of the two drugs. Follow your healthcare provider's advice every step of the way.

Contraindications and Important Interactions for Lactulose and Miralax



Avoid using it if you’re allergic to polyethylene glycol.

Also, avoid it if you have an intestinal blockage or a bowel obstruction.


Avoid using it if you're allergic to Lactulose.

Do not take Generlac, Enulose, Constulose and Kristalose.

Drug/Medication Interactions


  • Tramadol
  • Trazodone
  • Prednisone
  • Zofran
  • Albuterol


  • Aspirin
  • Avelox
  • Tramadol
  • AccuNeb
  • Abarelix

Food/Beverage/Supplement Interactions


  • Avoid drinking alcohol with it. It may lead to dehydration.
  • Avoid taking herbal supplements with it. They may increase the risk of dehydration.


  • Avoid drinking alcohol with it. It may worsen the laxative’s effects.
  • Do not eat fructose-containing food items.
  • Avoid taking antacids. They decrease the effectiveness of Lactulose.

Cost Comparison

How Much Do Lactulose and Miralax Cost?

Insurance covers both medications. So the price varies by certain factors such as:

  • Location
  • Pharmacy

The average retail price for Miralax is $17 for 17 grams of powder. The average retail price of Lactulose is $23.13 for 10 grams of oral liquid. These prices are exclusive of insurance coverage.

The price also varies by factors such as:

  • The condition
  • The prescription
  • The duration of treatment

The Popularity of Miralax and Lactulose

Miralax provides gentle relief from constipation. It is one of the best drugs to treat occasional constipation. Another reason why it’s popular is that you can dilute it in different liquids. The advantages of using this medication certainly outweigh the disadvantages. While other drugs can take a long time to work, Miralax shows results in just one to three days. In many cases, it doesn’t lead to any harsh side effects such as:

  • Bloating
  • Cramping
  • Sudden urgency

Lactulose, on the other hand, is a multitasker. It's a popular choice to treat chronic constipation. But it also treats hepatic encephalopathy. People also prefer it over other drugs because it comes as a sweet syrup. You can buy it from pharmacies and also use your prescription to get access.

It is therapeutically more effective. It is by far one of the best remedies for long-term or chronic constipation. There are many clinical trials recruiting volunteers to test these medications further.



Keeping all the information in mind, it’s reasonable to conclude the following:

  • Both drugs are effective for treating constipation. But their usage depends on the type and severity of the condition. Only a healthcare provider can determine the right dosage for you, keeping your symptoms in mind.
  • While both drugs have side effects, their benefits outweigh the costs. It’s important not to miss a dose. But it’s also important not to take extra medication to cover up.
  • Many insurance plans cover the cost of these medications.
  • The mode of delivery also varies by age and severity of the condition. The dosage may fluctuate if you're using a different mode of delivery (solution or oral in the case of Lactulose).

In many cases, healthcare professionals do not immediately prescribe these drugs. They may recommend dietary modifications. They may also suggest making other lifestyle changes to improve your symptoms. Only after these approaches have failed will they suggest using Lactulose or Miralax.