Lactulose Vs. Miralax


Lactulose and Miralax are two of the most commonly prescribed medications for anyone struggling with chronic constipation. Both have effectively provided relief from occasional or occasional to frequent bouts of constipation symptoms.

However, despite their potency, it is important to understand their differences before deciding which one may be right for you. Understanding how they work differently within the human body makes it much easier to choose a medication tailored to any specific need.

About Lactulose and Miralax

What Is Lactulose?

Lactulose is a synthetic sugar composed of two other sugars known as fructose and galactose. It was developed in the 1920s in order to treat constipation and is still used today for that purpose. It is made by the chemical reaction of lactose and an enzyme called β-galactosidase.

Lactulose is an effective laxative because it encourages bowel movements, softens feces, and draws water into the digestive tract.

In the case of hepatic encephalopathy, lactulose is useful for lowering the amount of ammonia created by bacteria in the stomach. This ammonia can build up and create neurological symptoms if not removed.

What Conditions Is Lactulose Approved to Treat?

Lactulose was approved by the FDA in 1997. It has since been approved for other treatments, including hepatic encephalopathy. Although approved by the FDA, there is still a need for more evidence to support its efficacy.

Lactulose is available in various forms, including liquid (syrup), powder, and tablet. The most commonly consumed form of lactulose is syrup form, as it is easy to take. The powder form is also available and can be mixed with water or other liquids. Lactulose tablets are less commonly used but may be preferred by some people with difficulty taking the liquid or powder forms.

Lactulose is approved to treat the following conditions;

1. Hepatic Encephalopathy

Hepatic encephalopathy is a neurological disorder caused by liver failure and the consequent accumulation of toxins that are normally excreted by the organ. These substances lead to symptoms such as altered mental status, confusion, disorientation, and coma.

2. Chronic Constipation

Chronic constipation is a health condition that affects the body's digestive system, characterized by difficulty passing stools due to slow food movement through the intestine.

Common symptoms include infrequent stools, hard stools, abdominal pain, and bloating.

It is important to note that lactulose can not treat hepatic encephalopathy but can ease the symptoms and mental status.

How Does Lactulose Work for Constipation and Hepatic Encephalopathy?

Because lactulose is non-absorbable synthetic sugar, it reaches the large intestine without being absorbed and broken down by the small intestine.

Once it reaches the large intestine, it is then metabolized by the bacteria present in the colon into monosaccharides. After these, monosaccharides are further broken down into volatile fatty acids, i.e., methane, nitrogen, and hydrogen.

Lactulose works in three stages to ease the symptoms of hepatic encephalopathy and reduce the production of ammonia.

Firstly, the sugars are metabolized in the colon, providing a laxative effect by increasing gas production and osmolality, decreasing the intraluminal pH. This helps in treating constipation.

Secondly, lactulose increases colonic bacteria's absorption of ammonia, which they use for protein synthesis. This mechanism converts gut bacteria-produced ammonia (NH3) to ionized ammonium (NH4+), which cannot permeate biological membranes, by lowering intestinal pH.

Lastly, the undissolved disaccharide inhibits intestinal glutaminase activity, blocking glutamine absorption and ammonia metabolism.

Although lactulose is widely believed to help patients with hepatic encephalopathy, it is considered unethical to refrain from the patients who need it, making it difficult for researchers to conduct placebo-controlled trials to study its effectiveness.

What Is Miralax?

Miralax is a common prescription and over-the-counter drug that is used for the treatment of occasional constipation.

It is an osmotic laxative that typically takes one to three days to experience relief from constipation symptoms after taking Miralax, and it is recommended as an effective long-term solution for occasional constipation relief.

The active ingredient in Miralax is polyethylene glycol 3350. Polyethylene glycol is derived from ethylene oxide and water. This compound can be dissolved in water, has no taste or odor, and is quite famous for relieving constipation.

In Miralax, PEG is formulated to be used as a laxative.

What Conditions Is Miralax Approved to Treat?

Miralax is approved by the FDA for the treatment of occasional constipation.

It is a condition during which a patient faces difficulty passing stool less than three times per week. It is caused by various factors such as diet, dehydration, and lack of physical activity.

The most common symptom of occasional constipation is a hardened, painful stool that can be difficult to pass. Other symptoms can include bloating, abdominal discomfort, and feeling like you have not completely emptied your bowels after using the toilet.

Although Miralax is not approved by the FDA for children, evidence suggests that it is safe for children to treat occasional constipation.

How Does Miralax Work for Occasional Constipation?

Polyethylene glycol 3350 is an osmotic laxative. It has too large molecules to be absorbed by the body, so it works by drawing water into the colon. This extra water softens the stool and increases its volume, which helps stimulate bowel movements.

Miralax is typically taken orally and should be dissolved in a liquid before ingestion. It usually takes one to three days to produce a bowel movement, and the dose can be adjusted based on individual needs.


How Effective Are Miralax and Lactulose for Treating Constipation?

Both Miralax and Lactulose can take up to 2-3 days to produce a bowel movement, and both are generally considered safe and effective for treating constipation. However, some evidence suggests that Miralax may have a more rapid onset of action and produce softer stools than lactulose.

Miralax and lactulose belong to the same category, but their mechanism of action is a mild difference. While Miralax works by increasing the amount of water in the stool, making it easier to pass. Lactulose works by the metabolism of bacteria in the colon to form acids that draw water into the colon, which softens the stool and makes it easier to pass.

A 2013 study published in the Journal of Pediatric Gastroenterology and Nutrition found that Miralax and Lactulose effectively treat constipation in children. However, the study noted that Miralax had a more rapid onset of action and produced softer stools than lactulose.

In a comparative efficacy study of lactulose, paraffin, and polyethylene glycol found that the laxatives were safe and effective, but Miralax was better tolerated and produced more complete bowel movements than lactulose and paraffin.

Dosage Information

How Is Lactulose Administered for Constipation?

Lactulose is available in different forms, including;

  • Oral solution.
  • Rectal solution.
  • Oral powder.

Lactulose Dosage Information

The dosage of lactulose can vary depending on the individual's age, the severity of their constipation, and other factors.

How Is Miralax Administered for Constipation?

Miralax is available is only available in the market in powder form.

Side Effects

Both lactulose and Miralax have their own side effects. Remember that if you face any of the below-mentioned side effects, immediately talk to your doctor and discontinue your medicine.

What Are the Most Common Side Effects of Lactulose?

The most common side effects of lactulose include the following;

  • Explosive diarrhea.
  • Swelling in legs.
  • Dizziness.
  • Disturbed breathing.
  • Tiredness and weakness.
  • Restlessness.
  • Bloating.
  • Cramps.
  • Twitching.
  • Mood changes.
  • Confused mind.
  • Loss of appetite.
  • Dry mouth.
  • Increased frequency in passing gas.
  • Nausea.

Are There Any Potentially Serious Side Effects of Lactulose?

Some of the serious side effects of lactulose include the following;

  • Fainting.
  • Stomach ache.
  • Medicinal reactions.
  • Tingling and itching on skin.

What Are the Most Common Side Effects of Miralax?

Some of the most common side effects of Miralax include the following;

  • Abdominal cramps.
  • Vomiting.
  • Stomach pain.
  • Diarrhea.
  • Dizziness.
  • Increased frequency of gas passing.
  • Loose stools.
  • Sweating

Are There Any Potentially Serious Side Effects of Miralax?

Some of the potentially serious side effects of Miralax include the following;

  • Dehydration.
  • Confusion.
  • Blood in stools.
  • Rectal bleeding.
  • Explosive diarrhea with blood.

Contraindications and Interactions

Warnings and General Precautions for Lactulose and Miralax

Lactulose is not recommended for long-term use, as it can lead to dependence and decreased bowel function over time. It is also inappropriate for individuals with certain medical conditions, such as diabetes, galactosemia, or lactose intolerance. People with diabetes should monitor their blood sugar levels closely while taking lactulose. People on a low-potassium diet or with kidney problems should use lactulose with caution.

Miralax can cause an imbalance of electrolytes, particularly sodium. People with kidney issues should use caution when taking Miralax. It is important to drink plenty of water as it as cause dehydration. It is recommended not to use Miralax if you have intestinal blockage.

Contraindications and Important Interactions for Lactulose and Miralax



Not recommended for people with lactulose allergies.

Lactulose is not suitable for people with galactosemia.


Not recommended for people with

It may cause allergic reactions if you are hypersensitive to medication.

Drug/Medication Interactions


  • Abarelix
  • AccuNeb
  • Tramadol
  • Avelox
  • Aspirin
  • Asenapine


  • Albuterol
  • Aspirin
  • Trazodone
  • Omeprazole
  • Gabapentin
  • Atorvastatin

Food/Beverage/Supplement Interactions


Drinking alcohol while taking lactulose can worsen its laxative effects.

Avoid taking antacids, as it may decrease the effectiveness of lactulose

It is recommended to avoid consuming large amounts of fructose-containing foods while taking lactulose like fruits.


Drinking alcohol while taking Miralax may increase the risk of dehydration and worsen its laxative effects.

Taking any fiber supplements with 2-4 hours of break is recommended to prevent them from interfering with Miralax's laxative effects.

Do not take any herbal supplements with Miralax. Herbal supplements, such as senna and cascara, can increase the risk of dehydration.

Cost Comparison

How Much Do Miralax and Lactulose Cost?

Both medications are covered by insurance, and prices vary by factors, including pharmacy and location. Lactulose is available for $23.13 for 10g of oral and rectal liquid and $15 in syrup form. Miralax is available for $17 for 17gm of powder without insurance.

The Popularity of Lactulose and Miralax

Miralax and lactulose rank highly among the millions of health products available today, with lactulose reaching number 372 and Miralax at 226 on the 2020 ratings list. This popularity is largely due to their effectiveness; both products are effective alternatives for treating constipation and gastrointestinal issues.



Lactulose helps draw water into the colon to help ease constipation. It can be used once or twice daily, but it may cause diarrhea and abdominal discomfort if it's not recommended. Miralax is a laxative that pulls fluid back into the intestine, making stool easier to pass. It's also easy to use; only one dose each day is needed. If you want an effective laxative with minimal side effects, Miralax is your best option; however, if you're looking for something with natural properties, look towards lactulose.