Pharmacogenetic testing: CYP2D6

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Learn about CYP2D6, a gene tested through pharmacogenetic testing to predict an individual’s response to certain medications.

Key points

  • CYP2D6 is a pharmacogenetic (PGx) gene that provides instructions for creating the CYP2D6 enzyme, a protein mainly found in the liver.
  • The results of CYP2D6 PGx testing can predict the metabolizer status of your child’s CYP2D6 enzyme, which can help their health-care team choose or adjust their medication and dosage.
  • There are many different medication classes and types that are affected by genetic variation in CYP2D6 including opioids, antidepressants, antipsychotics, non-stimulant ADHD medications, anti-nausea medications, antiarrhythmics, nerve disorder medications, and substrate reduction therapies.
  • There are four different metabolizer statuses for CYP2D6 as a result of genetic variation in the CYP2D6 gene: poor metabolizer, intermediate metabolizer, normal metabolizer and ultrarapid metabolizer.

Genes tested in pharmacogenetics

Genes serve as the instructions our bodies use to develop, grow and function throughout our life. In pharmacogenetics (PGx), genes are tested for their association with predicted medication response. Most genes analyzed in PGx testing provide instructions for enzymes. Enzymes are proteins in the body that help process medications by either activating them or breaking them down (metabolizing them). Genetic variations found in these genes can affect how quickly or slowly an individual processes a medication, influencing the medication’s effectiveness and potential side effects.

What is CYP2D6?

CYP2D6 is a gene that provides instructions to make the CYP2D6 enzyme, which is involved in the breakdown (metabolism) and activation of medications within the body. This enzyme is mainly found in the liver, which is where it processes certain medications, affecting how well they work and how long they stay in the body.

PGx testing of CYP2D6

Genetic variation—the natural differences in DNA sequences between individuals—can affect how different people process the same medication. Because of specific genetic variation, the CYP2D6 enzyme may work differently from person to person. 

The results of CYP2D6 PGx testing can predict how quickly or slowly your child is able to metabolize or activate certain medications, which can help their health-care team choose or adjust their medication and dosage.

Medications affected by CYP2D6

Currently, there are many different medication classes and types that are affected by genetic variation in CYP2D6. If your child’s enzyme is predicted to work slower or faster than the average population, it may affect how these medications work:

  • Opioids – medications that help with pain 
    • Codeine 
    • Oxycodone 
    • Tramadol 
    • Hydrocodone 
  • Antidepressants – medications that help with feeling sad or anxious 
    • Selective serotonin reuptake inhibitors (SRRIs)
      • Fluvoxamine 
      • Paroxetine 
    • Selective norepinephrine reuptake inhibitors (SNRIs)
      • Venlafaxine 
    • Tricyclic antidepressants (TCAs)
      • Amitriptyline 
      • Clomipramine 
      • Desipramine
      • Doxepin 
      • Impramine 
      • Nortriptyline 
      • Trimipramine
    • Serotonin modulator and stimulators (SMSs)
      • Vortioxetine 
  • Antipsychotics – medications that help with stabilizing mood 
    • Typical/first-generation antipsychotics
      • Haloperidol
      • Pimozide 
      • Zuclopenthixol 
      • Perphenazine 
    • Atypical/second-generation antipsychotics
  • Non-stimulant ADHD medications – medications that help with ADHD 
    • Atomoxetine 
  • Anti-nausea medications (antiemetics) – medications that help reduce nausea 
  • Antiarrhythmics – medications that help take care of your heart 
  • Medications that treat nerve disorders
    • Tetrabenazine 
    • Pitolisant 
  • Substrate reduction therapies – treatments for certain metabolic disorders 
    • Medications that treat Gaucher's disease (a genetic disorder where the enzyme glucocerebroside accumulates in cells)
      • Eliglustat 

The medications listed above are referred to by their generic names. You may hear your child’s medication called by a different brand name. Generic medicines and brand-name medicines share the same active ingredient and offer the same performance, safety and effectiveness. This medication list is also subject to change with increasing research on the CYP2D6 enzyme.

CYP2D6 metabolizer statuses

The PGx results for CYP2D6 are organized into metabolizer status categories, based on the predicted function of the enzyme. Patients may be categorized into one of four groups:

  • Poor metabolizer – reduced enzyme activity; your child may break down medication much more slowly than most individuals 
    • Your child’s health-care team may recommend starting with a lower dose of medication or switching to a different medication to ensure it works safely and effectively for your child.
  • Intermediate metabolizer – reduced enzyme activity; your child may break down medication more slowly than most individuals
    • Your child’s health-care team may recommend starting with a lower dose or maintaining a reduced dose to help ensure the medication works safely and effectively for your child.
  • Normal metabolizer – average enzyme activity; your child is predicted to break down medication at the expected rate
    • Most medications should work as expected at standard doses. 
  • Ultrarapid metabolizer – increased enzyme activity; your child may break down medication significantly faster than most individuals
    • Your child’s health-care team may recommend starting with a higher dose of medication or switching to a different medication to ensure it works safely and effectively for your child.

These statuses are not an indicator of your child’s health—they simply predict whether your child might need a different dose of medication or a different medication entirely. In addition to PGx test results, your child’s health-care team will still consider medical history and other factors to ensure the best treatment for your child.

To learn more about drug metabolism, metabolizing enzymes and the metabolizer status scale, see Genetics basics for pharmacogenetics. 

Why is my child’s PGx status important?

CYP2D6 is an enzyme that helps break down certain medications in the body. You can think of it like a drain in a pool that controls how quickly water flows out. The water represents medication.

  • If the drain is slow, water builds up. 
  • If the drain is too fast, water runs out quickly. 

Similarly, if your child’s CYP2D6 enzyme is slower or faster than average at breaking down certain medication, the medication might stay longer in the body (causing unwanted effects) or leave the body before it can work properly.

What is a prodrug?

Some medications, called prodrugs, need enzymes to make them work. Think of a glowstick—it does not shine until you crack/bend it. A prodrug is like a glowstick, and the CYP2D6 enzyme helps crack it to “turn it on”. Knowing your child’s CYP2D6 status helps their health-care team choose the right dose and type of medication for your child so it works properly and safely. 

Last updated: September 29th 2025