When you take a medicine (or drug), your body needs to find a way to use it.  Some proteins in your body break down (or metabolize) medicines.  Breaking down a medicine can make it more or less active, based on the kind of medicine.  If your body breaks down a medicine too fast or too slowly, this may cause the medicine to not work as well.  It may also cause a side effect.


The CYP2C9 gene gives instructions to your body to make a protein.  It is the job of the CYP2C9 protein to break down certain medicines.  These medicines include:

  • Some nonsteroidal anti-inflammatory drugs (NSAIDs) – used for pain relief
  • Siponimod – used to treat multiple sclerosis
  • Phenytoin and fosphenytoin – used for seizures


These are the medicines that we know of right now that are impacted by CYP2C9 gene test results.  Medical experts keep finding new data about which medicines are affected by gene test results.

By testing your DNA, we can find DNA differences.  This can help us to see how well the proteins in your body work to break down certain medicines. 


The results of your CYP2C9 gene test put you into 1 of 3 groups:


  • Normal metabolizer: People in this group are likely to have normal working CYP2C9 proteins.
  • Intermediate metabolizer: People in this group may have reduced activity of CYP2C9 proteins. 
  • Poor metabolizer: People in this group may have very little or no active CYP2C9 protein. 


The results of this test can help your doctor choose the right medicine and dose for you.