top of page

Laxatives Explained: Osmotic Laxatives – Part 2

Updated: Jan 12, 2021

Movicol, Lactulose (Duphalac), Microlax and constipation

Osmotic Laxatives (Stool Softeners)


Movicol is a prescription only osmotic laxative. It is made up of macrogol (also known as polyethylene glycol) which is not absorbed in the large intestine. Movicol attracts water and therefore draws water into the stool. This increases the stool volume. By increasing the stool volume, it creates pressure against the wall of the large intestine, and by neuromuscular pathways (messages sent from the muscles to the brain) it triggers motility (movement) of the large intestine. Therefore, it softens the stools and creates a propulsive movement in the large intestine which helps to move the faeces along until they are evacuated. Movicol can take up to three days before it has an effect on bowel movements.

Lactulose/ Duphalac

Lactulose, or sometimes more commonly known as Duphalac, is available both on prescription and over the counter. It is one of the most commonly bought laxatives over the counter. It is an osmotic laxative.

Lactulose is a type of sugar which is broken down by the bacteria in the large intestine into acids. These acids pull water out from the body and into the bowel which softens the stools and makes it easier to pass. The softened stools are increased in size which also helps to stimulate peristalsis (movement) of the colon and clear constipation.

However, as the intestinal bacteria feed on the sugar to break it down, this can produce unwanted side effects such as gas, bloating and abdominal pain.

Dose: For adults, the dose is 15-45ml daily. This can be taken in divided doses during the day.

Microlax Enemas

Microlax enemas are solutions that are inserted into the rectum and work by softening and lubricating the stools making them easier to pass. Unlike many of the other laxatives, these have a relatively quick effect, working in around 15 minutes. However, long term use of these enemas can cause irritation of the anal canal

Colon Hydrotherapy compared to Osmotic Laxatives

Similarly to Movicol, Lactulose and Microlax, Colon Hydrotherapy introduces water into the stool which softens and bulks the stool up. This also creates a pressure against the large intestine wall, causing bowel peristalsis (movement), aiding in the removal of stools. Colonics also help to clear the whole large intestine while microlax enemas only clear the lower part of the rectum. Unlike Movicol and lactulose which can take a few days to have an effect, colon hydrotherapy has an immediate effect at removing stools and impacted matter and can give instant relief.

Read the next part of the series that explains bulk forming laxatives you may find in a pharmacy and how they compare to colon hydrotherapy

Click here to book your colon hydrotherapy session today.


1. 2020. Introduction - HSE.Ie. [online] Available at: <> [Accessed 5 November 2020].

2. 2020. Laxatives. [online] Available at: <> [Accessed 10 November 2020].

3. 2020. [online] Available at: <> [Accessed 5 November 2020].

4. 2020. Lactulose: Laxative To Treat Constipation. [online] Available at: <,their%20brain%20(hepatic%20encephalopathy)> [Accessed 5 November 2020].

5. 2020. Lactulose 10 G / 15 Ml Oral Solution Sachets | SPC | Intrapharm Laboratories Limited | Medicines.Ie. [online] Available at: <> [Accessed 5 November 2020].

6. 2020. [online] Available at: <>


bottom of page