# Miralax vs Milk of Magnesia



## AD

I haven't been here in a while, but my problems are little changed from the last time. I don't have time to go into everything here, but I do have a question I'm hoping someone can answer.I want to know how Miralax (full 17g dose) differs from milk of magnesia (full 4 tbsp. dose). M.O.M. is the only thing that's worked somewhat for the past 11 years, but my doctor is telling me Miralax might help with the gas and bloating while weaning off the M.O.M. Unfortunately, I noticed the Miralax failed to do much after I got below 3/4 dose (3 Tbsp.) of milk of magnesia. Obviously, it wasn't doing much of anything since that was the minimum dose where M.O.M. ever did anything for me anyway.I got down to no M.O.M., and was left with a few drops of brown liquid the next day. But the Miralax is supposed to work the same way; is it not? It all just brings water in the colon? Then again, why does the milk of magnesia only take a few hours and the Miralax take 1-3 days? I've been on Miralax several weeks, even though just recently without milk of magnesia. Shouldn't it be working? Does whatever make Miralax work more slowly make it less effective?Mostly though, I just can't understand why there is such a big difference if the two laxatives are supposed to have the same mechanism of action.


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## anxietygirl

Hi,I'm sorry you're having problems. I don't know how much I can help.My docs at Mayo Clinic said to use Miralax every day. I learned very, very quickly that if I don't use it every single day I start the constipation cycle again. Miralax works just 'okay' for me but if I'm faithful to it every day, and sometimes use 1 1/2 doses in a day or something like that, it does a passable job.I don't remember for sure, but in one of my classes I'm pretty sure they said using M.O.M. more than they suggest can cause difficulties for your kidneys. That's due to some of the ingredients. Miralax is supposed to be safer and not cause extra work and pressure on the kidneys from what I understood. Unfortunately it can take longer.I hope you find a routine that works for you.


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## Kathleen M.

I don't know of a head to head as to exactly how much water is pulled in by that dose of miralax and that dose of Magnesium.Given that 400 mgs of Magnesium (the USRDA) is enough to cause diarrhea in some people it may be that the dose of magnesium in the MOM at full dose (a lot more than 400) is pulling in more water than the full dose of Miralax. The 400 mg dose is in people without diarrhea problems. Some with IBS-D are very sensitive to Magnesium.The advantage to Miralax is that you can up the dose to what you need with out risk of overdosing.While most people will clear any excessive Magnesium from the body, some people do not and if you up the dose enough long enough you may overtax your ability to clear it out of the body and screw up your heart rhythm. People with kidney issues are most likely to have this happen, but I'd imagine there is some dose that will do it to anyone.Miralax can cause the diarrhea in a couple of hours thing. It does at the doses used for cleaning out the colon for a colonoscopy.I'd guess the "full dose" of it for constipation is low enough that you aren't going to cause a flush out as that can set you up for more constipation when there isn't anything left in the colon for awhile. However it is safe at quite high doses (enough to make you run clear for several BM's) so I wouldn't be to concerned about upping the dose if you need to, or adding the USRDA of magnesium to it to see if that helps pull a bit of water in faster.K.


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## AD

I did actually take a magnesium supplement, though mostly only to compensate for the magnesium actually absorbed. I read some analysis somewhere and found that, coincidentally, about the recommended daily value is what is actually absorbed from a full dose of M.O.M. I can't speak for the unabsorbed magnesium.My doctor didn't say anything about other health problems such as with the heart or kidneys. My new doctor was recommending the switch because he said M.O.M. was "very bloating," even if it resulted in going to bathroom. Obviously not, if I'm even more bloated without it.I didn't know about Miralax dosage. It's been my experience that anything that works in days rather than hours is worthless. Maybe I should just try a higher dose. Do I need an extra 8 oz. water for each 17 grams? What is the colonoscopy prep dosage?Also, how can one be constipated if the colon has been emptied? I would think constipation should be measured by how full the colon is for how long.


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## Kathleen M.

The problem is the colon really isn't supposed to ever be completely empty, and for some people after an emptying everything out the first section of stool that finally gets in there seems to get even more water pulled out of it than it would if the colon had stool all along the tract. This makes the stool even harder, drier, harder to pass and it may even take longer between BM's then if you hadn't completely flushed the system.Normal transit time is up to 72 hours so it isn't normal to completely dump every last bit out of the colon, that isn't the natural state and it doesn't seem to reset people to normal stooling afterward. If it did all you would need to do for constipation is a colonoscopy prep. It can take several days to pass a BM after a prep depending on your transit time, even when the stool is normal.Most people with constipation have normal transit times. Constipation can be either transit time, or stool consistency, or both.For a complete colon cleanse (so passing water for the last few stools) you do 4 liters at 60 grams per liter.I would increase the water with the increased dose of the miralax. You want to make sure there is enough water for the osmotic to keep in the stool.


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## AD

That still leaves me wondering what officially qualifies as "constipation." Frequency is a poor measure if only a couple of drops come out.I suspect I'm just particularly sensitive to small amounts of anything anywhere in my colon. Before this whole thing started, I wouldn't know if I hadn't gone to the bathroom for a week. I only thought it was a problem if I was having trouble pushing something out. Now, almost 11 years later, I cannot endure the day if I don't go substantially every morning due to the outward pressure against my abdomen. It's quite visible too.Anyway, I'd vomit if I consumed 4 liters of liquid! Although I drink 8-10 cups of water a day, too much liquid too fast is very nauseating for me, probably more than it is for most other people. I do not think my stomach could hold down much more than I drink now.I'm not sure how to adjust the Miralax. If I used more than 17 g, I'd assume a powder-to-water ratio of around 17 g per cup of water. If so, 34 grams would be the most I could do (within 1/2 to 1 hour). I'll probably have to work with my doctor on this and take the M.O.M. until then.Thanks for the info!


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## Kathleen M.

I wouldn't do colonoscopy prep amounts on any sort of regular basis, only when you need to be squeeky clean for a test.However you might do the Miralax 2x a day at 17 grams per dose and see if that is better than 1 time a day. Given that people tolerate much larger doses for a colonoscopy prep I don't think there is much risk of taking it two or three times a day at the full dose.There isn't much risk of adding more, and spreading it out between meals may work better than trying to do one large dose to keep all the stool moving.K.


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