How Prilosec works

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Regular Member

Date Joined Dec 2013
Total Posts : 40
   Posted 1/1/2014 11:24 AM (GMT -6)   
I've been on Prilosec OTC every day since 2007 (Prevacid before that). I'm still very sick so I'm doing some research and found some interesting information about Prilosec, which may or may not be the same for other PPI's as well.

According to the Prilosec OTC website (, one pill (20mg) blocks around 60% of stomach acid. But a half pill (10mg) only blocks 20%. Interestingly, higher doses (30mg to 80mg) still block only 60% of the acid, which means that higher doses are not more effective than the regular dose. So why do I think I feel better when I double my dose? Maybe it's the placebo effect? Although when I double my dose, I don't take 2 pills at the same time, I take 1 in the morning, and the second one I'll take later that night. The "duration of action" of one pill is 24 hours.

Also, the pills are enteric coated, so splitting the pill in half reduces its effectiveness because stomach acid breaks down the chemicals so they don't work as well. Because of the coating, the pills only start to work when they reach the less acid environment of the duodenum, which can take a half hour to 3 hours to start working.

The most common adverse effects are headache and diarrhea, but in all the years I've been on it I've never had those side effects.

Hope this is helpful!

Veteran Member

Date Joined Oct 2009
Total Posts : 4970
   Posted 1/1/2014 4:41 PM (GMT -6)   
librooks -

The pills don't actually work inside the stomach but rather from the blood stream. That's why you have to take them 1/2 hour to an hour before eating, and then you must eat or they don't work well. Duration of action for most PPIs is only about 8 hours, although duration of activity (some of the action) may be up to 3 days. Half-life tells you nothing because the drug is eliminated in just a couple of hours.

I never got worthwhile relief from Prilosec, although many others do. I only had relief from Nexium and Aciphex. I got no extra relief from taking my PPI twice a day.

The capsules are enteric coated, but at least Nexium can be opened and sprinkled on applesauce if necessary. The granules must not be chewed.

If you aren't getting adequate relief from one PPI, I would suggest asking your gastroenterologist for a prescription for a different one.

Regular Member

Date Joined Jul 2012
Total Posts : 190
   Posted 1/2/2014 3:17 PM (GMT -6)   
Librooks and Alcie, the workings of PPI's is fascinating, to those who take them every day.

Personally I think they get an undeserved bad press. Yes there are some known problems with their long term use, but all in all, we are all better off with having them available, at least as an option.

Thanks for the thread.
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