David asked
Are Metamucil and Miralax the same?
At a glance
- Metamucil (psyllium fiber) is used for constipation and can also reduce cholesterol levels. Miralax is used for constipation, to treat fecal impaction and as a pre-colonoscopy bowel preparation.
- Metamucil is generally dosed around 2.4 grams, one to three times daily. Miralax is dosed as 17 grams once daily for constipation, with higher doses used for colonoscopy preparation.
Answer
Metamucil and Miralax are not the same. Metamucil contains psyllium fiber while Miralax isn't a fiber at all, but rather an osmotic laxative that contains polyethylene glycol 3350 (PEG 3350).
Key differences between them are discussed below.
How They Work
Metamucil
Metamucil contains psyllium fiber, a 'bulk-forming laxative' which is obtained from the seeds of Plantago psyllium.
'Bulk-forming laxatives' like Metamucil work by absorbing liquid in the GI tract.
This absorption of liquid causes expansion of the stool, which helps to facilitate movement (i.e. motility) in the intestines. The absorption of water can also help to soften the stool.
Bulk-forming laxatives are often the agents of choice as initial therapy for most forms of constipation according to medical guidelines. This is due to their safety and the fact that fiber is a naturally occurring and a needed part of our diet for gastrointestinal health.
Miralax
Miralax contains polyethylene glycol 3350 (PEG 3350), which is classified as an osmotic laxative (not a 'bulk-forming laxative like Metamucil).
Osmotic laxatives work by drawing water into the intestines. Water is then bound and retained within the stool. The overall effect is softened stool consistency, increased stool frequency, and easier bowel movements.
A key difference in the mechanism of action between Miralax and Metamucil is that Miralax doesn't typically cause expansion of the stool, but rather softens it by increasing the water content.
High doses of Metamucil can sometimes cause impaction (as the stool will expand). High doses of Miralax will generally have a laxative effect, which is why it is often used for pre-colonoscopy bowel prep.
Side Effects
Metamucil
Side effects with Metamucil are uncommon but can include gas, abdominal cramps and bloating. It should be discontinued if abdominal pain or vomiting occurs.
Swelling of the throat, choking, or shortness of breath can occur if insufficient liquid is taken with psyllium, so each dose should be administered with one full glass of liquid to avoid obstruction.
Miralax
Excess gas, bloating and nausea may occur, but are less frequent than with Metamucil. Higher doses may produce diarrhea and increased stool frequency.
In the next sections, I discuss how both Metamucil and Miralax work
Excessive use can cause electrolyte imbalances and dehydration due to fluid loss.Final Words
Both Miralax and Metamucil can be taken daily and are available over the counter.
Metamucil is generally treated as a 'first-line' option for constipation while Miralax is often reserved for cases of chronic constipation.
References
- Management of Constipation in Older Adults. American Family Physician
- Medical Management of Constipation. PubMed
- Miralax Monograph. DailyMed
- Effect of psyllium (Plantago ovata) fiber on LDL cholesterol and alternative lipid targets, non-HDL cholesterol and apolipoprotein B: a systematic review and meta-analysis of randomized controlled trials.. PubMed
