Pharmacogenetics : Drug Intolerances and Genes

February 11, 2014  |  Blog, Drug Intolerance

When you look in the dictionary under ”adverse drug reaction” you will find my name. But a new world of pharmacogenetics (that uses genes to determine drug intolerances) has changed all of that. You see we all have our own bio-individuality.

First a little background.

In 2007 I had a CT-Scan and had an adverse reaction to the contrast. Then another. And another. I was prescribed a series of medication to deal with the severe adverse reactions, but developed severe adverse reactions to the medications, prescribed for the adverse reactions. It caused a histamine tornado in my body.

By 2011 all medication was withdrawn, after consulting a clinical pharmacologist, and I was given a letter to carry stating that medication was only to be used sparingly in an emergency. Since then it has been a “russian roulette” when I take medication.

But all of that has changed thanks to 23andME.

In 2013, unaware that genetic testing was available in Australia, or really what I was looking for, I spat into a tube and sent my dna to 23andMe. About 2 weeks later, I was able to download my genetic blueprint. I then ran the data through a limited report writer on which showed that I had a mutated CYP2D6 gene.

But that was not the whole story.

When I showed it to my specialist, and asked him what he knew about CYP2D6, luckily he had attended a lecture by Professor Les Sheffield (who is an Australian geneticist specialising in drug tolerance), and suggested I call him. His company is

That is where I had my break-through.

I spoke to Professor Sheffield, I provided him with my 23andMe results, and I agreed to redo the saliva test for four genes.

The genes that were tested were CYP2D6, CYP2C19, 2YP2C9, and VKORC1, which are responsible for metabolising over 50% of all commonly prescribed medications, including Phenergan and Codeine. There is also a high cross over for DAO inhibiting and histamine releasing drugs.

Where genes were tested by both 23andME and GenesFx the results were the same, and those results explained precisely the adverse reactions to drugs in the past, but here are a few things that you should know about the difference between 23andMe and GenesFx:

Genes Tested1 Million Only of the 10 MillionDNAdose tests for the common abnormalities in 4 genes. ?CYP2D6, CYP2C19, 2YP2C9, and VKORC1 *
CYP2D6, CYP2C19, CYP2C9, and VKORC1 genesPortion OnlyTests All Common Abnormalities in CYP2D6, CYP2C19, CYP2C9, and VKORC1 Genes
Interpretation ReportNone (Limited until 2013)Over 50% of All Drugs**
Services OfferedGene Saliva TestingCheek Brush or Blood Test
Medical Reporting:
- % of Gene Working
- Drugs Affected
- Likely Tolerance (and Recommended Dosage)
- Genetic Counselling
- Pharmacist Advisory Service
- Card to Carry for Emergencies
CostUS$99 plus shippingAus$195-270 plus shipping

* Other genes are thought to be involved in metabolising some drugs. For example, an incomplete list of drugs not tolerated with histamine intolerance based on published research is here. There is, however, a high degree of cross-over with the CYP2D6, CYP2C19, 2YP2C9, and VKORC1 genes.

** It is not known how some drugs work. It is likely that the percentage of medications covered by genetic testing will increase over the next 5 – 10 years.

So how has this helped?

Medications can be a significant trigger with histamine intolerance. Yet they can also be an important part of the treatment. Pharmacogenetics has enabled my specialists to tailor my medication to more effectively treat me.  For example, Phenergan, an anti-histamine with a long record of safe and effective use, is metabolised by CYP2D6, whereas Zertec is not.

Even without histamine intolerance there is a risk with any medication of an adverse reaction based on your genetic profile. It is my experience that drug intolerances are a specialist area, that doctors have limited training in this area, and that pharmacogenetics is a new (but widely accepted) area of medicine.

The report that I received from GenesFx provides a very clear colour coded report that is easily understood by both my doctor and myself. A sample of the report is here, although my recommendations for future medication was very detailed and over one page long.

If you have a history of adverse reactions to medication, or a hyper-sensitivity disorder, then your genes may just hold the answer. They certainly did for me.


Addendum: I have subsequently had the privilege to meet with Professor Les Sheffield and get a genetics lesson and I hope to share a little more soon. Genetics has a very precise language which is complicated and in this article I have purposefully just calling everything genetic ‘genes’.

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  • chrissy

    Have just sent off to do this. I am in the UK, so will take some time, hope to report back to you my results. Thank you for blogging this. I had never heard of it before.

  • Johan Olsen

    Great blog post Alison Could use this info. Did you know that Livewello just added a Pharmacogenomic tool?

    • No – thanks for letting me know. Although I have to write up that I am finding some of the online reports unreliable and highly recommend getting the specific test. I have seen a lot of MTHFR Support reports that turn out to be wrong. But thanks for letting me know; will hop on over and check it out!

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  • dkaj

    Hi Allison, would you recommend doing both tests – 23 and ME along with the Drug tolerance testing or could a person just do the drug tolerance test?? I’d hate to pay for both out of pocket. Also, can histamine intolerance and mast cell issues causes swelling in the bowel that makes it shut down for a good week. This has happened to my dd with food reactions and once that food hits the intestines, then she can not go to the bathroom. I’m almost wondering if her bowel is swelling shut. I’m thinking these are histamine reactions to certain foods/ ingredients – she has leaky gut also – but not IGE allergic at this time. Just curious about your thoughts on this and if you have heard of this with other clients. Any info would be greatly appreciated.

    • If drug intolerances are an issue then get the drug tolerance test as 23and Me does not cover the key genes for this. Here is my view; Histamine can be a symptom. I focus on the basics first; gut, methylation etc. If she has gut issues then that is where to start.

  • K.G.D.

    Hi Alison, I live in the U.S. I contacted GenesFX, who said they are not able to collect samples outside Australia. Do you know of companies in the U.S. who can do similar tests/interpretations? One I know of, Genomind, seems to primarily be concerned with psychiatric conditions and drugs. Thanks!

    • Hi K.G.D. I am aware of the genomind test but understand there is another test that one of my clients had under her insurance. I will find out their name and revert back to you.

      • K.G.D.

        Wonderful! Thanks so much for your help!

  • loretta harmes

    Hi Alison, unfortunately genesfx doesn’t currently ship to the UK. I am waiting for a response back from IDgenetix that you have suggested below, but I don’t think they ship to uk either. I have found a company called genelex in USA (who I’m also waiting for a response back from) and wondered if I could ask your opinion on this company and also if you have any suggestions of companies who ship to UK or are in the UK. I’m a tad worried about having to opt for a different company that you haven’t suggested.

    P.S….your website is extremely helpful!


    • Thankyou. Chase Lodge are now doing this test using a us company. The company they use is also used by some of the top mastcell doctors.

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