At a glance
Miralax (polyethylene glycol, or PEG) and lactulose are both osmotic laxatives — medications that soften stools by drawing water into the bowel. They are commonly used by people managing constipation, particularly alongside conditions like anal fissures, haemorrhoids, and post-surgical recovery where soft stools are essential.
This guide compares the two, covering how each works, what people commonly report about using them, and how to decide which might be more suitable for your situation.
How they work
Miralax (PEG)
Polyethylene glycol is a synthetic compound that is not absorbed by the body. It passes through the digestive system and draws water into the bowel by osmosis. This increases the water content of stools, making them softer and easier to pass.
PEG is available under various brand names:
- Miralax (US)
- Laxido, Movicol, CosmoCol (UK)
- Macrogol (generic)
Lactulose
Lactulose is a synthetic sugar that cannot be digested or absorbed in the small intestine. It passes into the large intestine where it draws water into the bowel (osmotic effect) and is fermented by gut bacteria (which produces gas).
Lactulose is typically available as a sweet liquid solution.
Comparing the two
Effectiveness
Both are effective osmotic laxatives. People describe similar stool-softening results from either medication when used at appropriate doses. The difference tends to be in the side effect profile rather than the effectiveness.
Bloating and gas
This is the most commonly discussed difference:
- Lactulose is significantly more likely to cause bloating, gas, and abdominal discomfort. The fermentation by gut bacteria produces gas, and this can be uncomfortable, particularly when starting the medication or at higher doses.
- Miralax (PEG) is not fermented and typically causes less bloating. People describe it as “gentler on the stomach.”
For people who are already dealing with anal conditions where straining and pressure are problems, the additional bloating from lactulose can be particularly unwelcome.
Taste and palatability
- Lactulose has a sweet, syrupy taste that many people find unpleasant over time. It is a thick liquid that some describe as cloying.
- Miralax (PEG) is a powder that dissolves in liquid. Most people describe it as having little or no taste. It can be mixed into water, juice, or other drinks.
Dose adjustment
Both can be dose-adjusted to achieve the desired stool consistency:
- Miralax: Typically one sachet or measured dose daily, adjusted up or down
- Lactulose: Usually started at a specific dose (often 15 to 30ml) and adjusted based on response
People describe PEG as slightly easier to fine-tune because the powder can be measured precisely and dissolved in varying amounts of liquid.
Speed of action
Both typically take one to three days to produce an effect when first started. Neither is a rapid-acting laxative — they work by gradually changing stool consistency rather than stimulating an immediate bowel movement.
What people commonly prefer
The pattern across many accounts is clear: Miralax (PEG) is more commonly preferred, primarily because of the lower incidence of bloating and the neutral taste. However, lactulose has its advocates, particularly:
- People who respond well to lactulose without significant gas
- Those who prefer a liquid format
- Situations where PEG is not available or not suitable
- Certain medical contexts where lactulose is specifically recommended
Neither is objectively “better.” The right choice depends on individual tolerance and preference.
Practical tips for either
- Start at a low dose and increase gradually — sudden introduction of either can cause cramping
- Stay well hydrated — osmotic laxatives draw water into the bowel; you need to replace it
- Be consistent — daily use produces more predictable results than occasional use
- Give it time — allow several days to assess the effect before adjusting the dose
- Keep a stool diary — tracking consistency and frequency helps you find the right dose
- Combine with fibre — osmotic laxatives and fibre work well together, but introduce them at different times to manage bloating
When to talk to your clinician
Discuss your laxative use with your clinician if:
- You are not seeing improvement despite consistent use
- You are experiencing significant side effects — severe bloating, cramping, or diarrhoea
- You need to use the laxative long-term and want to ensure this is appropriate
- You are managing a specific condition and want to know which option is better suited
- You are taking other medications and want to check for interactions
When to seek care
Contact your clinician if you experience:
- Severe abdominal pain or cramping
- No bowel movement for several days despite laxative use
- Blood in the stool
- Signs of dehydration — dizziness, dry mouth, dark urine
- Any symptoms that concern you