Field of Science

One purple pill is much like another

One purple pill is much like another, perhaps even more than you might think. You can't open a magazine these days without seeing an ad for "the purple pill", Nexium. The original purple pill, Prilosec, was the number one selling prescription drug in 2001. A proton pump inhibitor, it stopped the production of acid in the stomach at a different step than earlier heartburn drugs such as Zantac. Patent protection for Prilosec expired that year, and Nexium was introduced with much fanfare. The FDA approval was based on the argument that Nexium was more effective than Prilosec. Now for the chemistry trivia: Nexium is exactly the same molecule as Prilosec.

To understand the relationship between Nexium and Prilosec, you need to know that many organic molecules come in mirror-pairs. The molecules have exactly the same structure, but are mirror images of each other. Your hands are a good example of this kind of mirror pairing, and in fact the chemical term describing this phenomenon, chirality, comes from the Greek for hand.

Many biological systems show a preference for one mirror image over the other. For example, all the proteins in your body are made up of amino acids which exist in these mirror pairs. Naturally occurring proteins all use only one of the two mirror images, called the L form. Perhaps the most striking example is that of spearmint and caraway oils. Rye bread and spearmint gum taste very different, but the molecules responsible for the taste are identical except that they are mirror images of one another.

Back to Nexium and Prilosec. The active compound in Prilosec is omeprazol, which comes in two forms, R-omeprazol and S-omeprazol. The R and the S come from the Latin for right and left - just like the hands - and indicate that this is a pair of identical mirror images. Both R-omeprazol and S-omeprazol are effective in reducing heartburn, but S-omeprazol is about 4 times as effective as the R form. Prilosec contains a 50/50 mixture of the R and S forms, Nexium is pure S. So 20 mg of Prilosec is equivalent to 12.5 mg of Nexium (10 mg of S + 10 mg of R/4). The prescribing literature on Nexium obscures this fact, giving a new name to S-omeprazol: esomeprazol. Get it? "es"omeprazole.....

If you want to learn more about chirality, check out Prof. Jean-Claude Bradley's organic chemistry lecture. Lecture 16 introduces chirality. The lecture is available as a podcast or streaming video.


  1. Very cool stuff here Michelle. You've got a great blog going. I like the last two posts especially. I'm always yelling at the drug commercials on tv. It's nice to know some of the chemistry behind all this proliferation of drugs--and the patent issues as well.

  2. Very interesting blog. I found it when I did a search of Nexium vs. Prilosec. Please keep on posting.

    It is amazing to me what companies will do to make a buck. I used to work for large medical companies and saw first hand these discussions by management on how to maximize profits. What ever happened to the original intent of helping people?

    This is part of the reason I'm back in academia. There must be a better way to get drugs and devices to patients, and I intend to do my best to figure this out.

  3. Wait, if all the naturally occuring proteins are S molecules, then are both rye and carroway S molecules? How then are they opposites? I'm confused!

  4. Ah...good point! Rye and caraway flavors aren't proteins...they are just small molecules that your body reacts to.

  5. Ah! That certainly rectifies everything then :) Thanks for the response!

  6. I have a very rare disease and have been on Nexium for the past 7 years. I found out today that my insurance no longer covers it (it was all ready costing me a $60 copay). I went to buy them on my own and found out they went from $6.00 to $9.00 a pill. I was mortified. I have tried everything else and nothing else works. After reading this, I was wondering if I took 3-1/2 Prilosecs, would that do the trick? I have tried them before, but may be I wasn't taking enough. I haven't priced them lately, I am wondering if it would be cost efficient to take 3-1/2 a day and would that cause more side effects? I will be on them for the rest of my life. Any suggestions?
    PS. Nexium has been out over 7 years, were is the generic all ready??

  7. Anonymous - curiously, what is the condition you suffer from if you don't mind me asking...would it be achalaysia? I too would like to know the answer to the question you asked.


  8. Anonymous - curiously, what is the condition you suffer from if you don't mind me asking...would it be achalaysia? I too would like to know the answer to the question you asked.


  9. My name is John Diamond and i would like to show you my personal experience with Nexium.

    I am 58 years old. I have bee taking Nexium on and off for 2 years. For the last 3 months I have been taking 1-40mg daily. I have been cycling for 10 years riding avg. of 150 miles a week. I noticed this year I had no energy. Was riding 4 to 5 times a week and could hardly go. A fellow rider told me last week about the vitimin B absorbtion problem and other side effects he had from Nexium. I quit the Nexium last week and I could really tell the differance in my energy level. I was riding regularly and watching what I ate but could not see a weight loss. Now I see that others are having the same problems. I had never had the itchy rectum problem in my life untill a couple of months ago, when I started back on the Nexium on a regular basis.

    I have experienced some of these side effects-
    Fatigue, weight gain, itchy rectum

    I hope this information will be useful to others,
    John Diamond

  10. Hey, HisGloryFillsThe Earth. Prilosec and Nexium are the essentially the same, but Prilosec is available as a generic and over the counter. You will spend more by buying it over the counter. Get an RX for Prilosec generic, and it will cost you $4 at Many pharmacies. Also, if you are on Medicare, ask the pharmacist not to bill Medicare. You get it for $4 whether you have insurance or not, and the additional billing of your insurance will push you further toward the "doughnut." This is another instance of waste and fraud. Also, why pay a deductible for mail-order generic drugs when you can get a month's supply for only $4 (Wal-Mart, Target, Walgreens, and other pharmacies).

  11. To answer Bambu's question. My husband has achalaysia and is only able to take Nexium for relief of burning. He's tried every other pill with no luck. I've heard prilosec actually closes the esophagus which is exactly opposite of what a person with achalaysia would want.


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