Key takeaways
Lactulose (Constulose) and psyllium (Metamucil) are both used to treat constipation, but they work in different ways and have distinct characteristics. Lactulose is a prescription-only osmotic laxative that draws fluid into the gut to soften stools, while psyllium is an over-the-counter fiber laxative that helps stools absorb water, making them bulkier and easier to pass. Lactulose can take up to two days to work and may cause side effects like stomach pain and gas, whereas psyllium can take 12 to 72 hours and may cause bloating, especially when you first start. Lactulose is not suitable for people who are lactose intolerant or on a low-galactose diet, while psyllium must be taken with plenty of liquid to avoid choking. Additionally, lactulose is available as a liquid, whereas psyllium comes in various forms, including flavored powders and capsules.
