At a glance
Milk of magnesia and Miralax are two of the options people compare most when they need softer stools, often with a fissure or after anal surgery.
- Both are osmotic. They draw water into the bowel. Neither stimulates the bowel muscle the way senna or bisacodyl does.
- Milk of magnesia is magnesium hydroxide. It is a chalky liquid, usually mint flavoured. People describe it as quick, sometimes abrupt.
- Miralax is polyethylene glycol, also called macrogol. The UK equivalents are Movicol, Laxido, CosmoCol and own-brand macrogol; most UK versions also contain salts, which Miralax does not. It is a tasteless powder mixed into a drink. People describe it as slower and steadier.
- Neither one is right for everyone. Many people try both before settling.
We do not give amounts here. Follow the label, and ask a pharmacist if you are unsure.
How each one works
Milk of magnesia. Magnesium hydroxide is poorly absorbed, so most of it stays in the bowel and holds water there. It also tends to trigger bowel activity fairly quickly. Many people take it in the evening and go the next morning.
Macrogol (Miralax, Movicol, Laxido). Polyethylene glycol is a large molecule that the body does not absorb. It binds water and carries it through the bowel, so stools stay softer. It builds up over a few days rather than acting in one go. Some UK versions also contain salts to help keep fluid balance steady.
Both are generally considered gentler than stimulant laxatives. Both can cause loose stools if the amount is more than your body needs.
How people compare them
| Milk of magnesia | Macrogol (Miralax, Movicol, Laxido) | |
|---|---|---|
| What it is | Magnesium hydroxide liquid | Polyethylene glycol powder |
| How people describe timing | Often within hours, commonly taken at night | Gradual, usually one to three days to settle |
| Predictability | Described as more “all or nothing” by some | Described as easier to fine-tune by many |
| Taste and texture | Chalky, minty, a love-or-hate taste | Tasteless once dissolved, some notice a texture |
| Side effects people report | Cramping, urgency, watery stools | Bloating, wind, sometimes loose stools |
| Main caution | Kidney problems, medicine interactions | Bloating, fluid balance in some people |
Timing. The speed of milk of magnesia is the reason people reach for it, and also the reason some people avoid it. A recurring description is being “on standby” the morning after. Macrogol is slower, so people talk about waiting a few days to see where things settle.
Predictability. Many people with fissures prefer macrogol because they can adjust it in small steps and the effect is steadier. Others find milk of magnesia reliable once they know how their body responds. A recurring report is that milk of magnesia seemed to stop working as well after weeks of use, while others have used it for years without that problem.
Taste. Milk of magnesia’s chalky taste puts some people off. Macrogol is often described as having no taste in juice or squash. A few people notice a slightly slippery texture.
Cramping. Cramps and gurgling are more often mentioned with milk of magnesia, especially early on. Bloating and wind are mentioned more often with macrogol. Some people get neither.
Why some people alternate or combine
Some people describe switching between the two, or using a small amount of one alongside the other. The reasons they give:
- Macrogol keeps things steady, and milk of magnesia is kept for a day when things feel slow
- One stopped feeling as effective, so they swapped for a while
- Macrogol caused bloating, so they reduced it and added a little milk of magnesia
- Their surgeon suggested one first and the other as a back-up
Combining laxatives raises the chance of watery stools, cramping and dehydration. Check with a pharmacist or GP before you combine them. This matters most if you have kidney problems or take other medicines.
The lessons people share
These come up again and again across many anonymised accounts.
- The first try surprised a lot of people. The most repeated lesson about milk of magnesia is that the first dose had a stronger effect than many expected, with hours of loose stools. Many wish they had asked a pharmacist what to expect and how to start.
- Watery is not the goal. People with fissures often describe watery stools as stinging and irritating. Soft and formed is the aim, not liquid.
- Fluids matter. Both work by moving water into the bowel. People describe feeling drained and thirsty after a loose day.
- Timing is personal. Some take milk of magnesia at night to go in the morning. Others split macrogol through the day. There is no single right routine.
- Doctors’ views differ. People report being told different things about long-term use by different clinicians. Ask yours directly what they recommend for you.
- Your body changes. What worked during a bad flare might be too much once things settle. People describe stepping down with their pharmacist’s or GP’s help.
Questions to ask a pharmacist or GP
- “Which of these suits my health and my other medicines?”
- “Is it okay to use either one for several weeks?”
- “Can I use both, and if so how?”
- “What should I do if my stools go watery?”
- “How should I step down when I’m ready?”
When to seek care
Get urgent help (go to A&E or an emergency department, or call 999 in the UK or 911 in the US) if you have:
- Heavy bleeding that will not stop
- Severe tummy pain, a swollen tummy or vomiting, especially if you cannot pass stool or wind
- Fainting, confusion or a racing or irregular heartbeat
See your GP or call NHS 111 soon if you have:
- Watery diarrhoea that lasts more than a day
- Signs of dehydration, such as dizziness, dark urine and a dry mouth
- Fever, swelling or discharge around the anus
- Pain that is getting worse rather than better
- Bleeding alongside unexplained weight loss, ongoing tiredness, or a family history of bowel cancer. Do not wait for a routine slot; say this when you book.
Book a routine GP appointment if:
- You have needed a laxative most days for more than a few weeks
- Your bowel habit has changed and stayed changed. This matters at any age, and more so over 50