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 DPYD gene gives instructions to your body to make a protein.  It is the job of the DPYD protein to break down certain medicines.  These medicines include some anticancer treatments, called fluoropyrimidines.  Examples of these medicines are:

  • Capecitabine
  • Fluorouracil (5-FU)

These are the medicines that we know of right now that are impacted by DPYD 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 DPYD gene test put you into 1 of 3 groups:

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


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


If you are an intermediate or poor metabolizer, you may have a higher chance of side effects when taking fluoropyrimidines.  Based on your result, your doctor may choose to prescribe a lower dose or a different anticancer medicine.