CYP2D6 Gene: How Your DNA Affects 25% of All Medications

Educational Content Disclaimer

This article is for educational purposes only and does not constitute medical advice. The genetic information discussed here is based on consumer DNA chip data, which is not equivalent to a clinical pharmacogenomic test. Consumer DNA chips (23andMe, AncestryDNA, etc.) do not reliably capture all CYP2D6 variants, copy number variations, or star alleles required for clinical interpretation.

Do not change, stop, or adjust any medication based on this article or your raw DNA data. Always consult a licensed physician, pharmacist, or clinical pharmacogenomics specialist before making any medication decisions.

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What Is the CYP2D6 Gene and Why It Matters

Your liver does far more than filter toxins — it runs a sophisticated chemical factory that breaks down roughly 25% of all prescription drugs on the market. The CYP2D6 gene (cytochrome P450 2D6) is one of the most important workers in that factory.

CYP2D6 encodes an enzyme responsible for metabolizing a wide range of medications: many antidepressants (SSRIs and tricyclics), antipsychotics, beta-blockers like metoprolol, opioids like codeine and tramadol, and tamoxifen — a breast cancer treatment used by millions of women. When this enzyme works differently than expected, the effects of those drugs can be amplified, reduced, or in rare cases, dangerous.

What makes CYP2D6 unusual is how variable it is. Unlike most human genes, CYP2D6 is extraordinarily polymorphic — meaning it comes in dozens of functional variants, called "star alleles" (*1, *2, *4, *10, and many more). Some people carry gene duplications that produce too much enzyme. Others inherit non-functional copies that produce almost none. Most fall somewhere in between. This variation is largely determined by ancestry.

The practical question for someone with a raw DNA file from 23andMe, AncestryDNA, or MyHeritage: Can I see my CYP2D6 type in my data? The short answer is: partially — and with important caveats we'll cover in detail.

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Metabolizer Types: Poor, Intermediate, Normal, Ultrarapid

Pharmacogenomics — the study of how genes affect drug response — classifies people into four CYP2D6 metabolizer types. Your type depends on the combination of star alleles you inherited from each parent.

Your phenotype (which bucket you fall into) is determined by the combination of two alleles — one inherited from each parent. A person who inherits *1 (normal) from one parent and *4 (non-functional) from the other is typically an Intermediate Metabolizer. Two copies of *4 generally result in Poor Metabolizer status.

Ultrarapid Metabolizers are particularly interesting: they usually carry gene duplications, meaning they have three or more functional copies of CYP2D6 instead of the usual two. These duplications are more common in people with North African, Middle Eastern, or Ethiopian ancestry — and they're notoriously difficult to detect with consumer DNA chips.

Worldwide, roughly 5–10% of Europeans are Poor Metabolizers. Ultrarapid Metabolizers account for 1–2% in most European populations but up to 29% in some Ethiopian cohorts.

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CYP2D6 and Common Medications

The list of drugs affected by CYP2D6 is long. Here are the major categories and what your metabolizer status can mean for each:

It's worth noting that CYP2D6 doesn't work in isolation. Many drugs inhibit CYP2D6 — including fluoxetine and paroxetine themselves. Taking one of these can temporarily turn a Normal Metabolizer into a functional Poor Metabolizer. This is called phenoconversion, and it means your genetic result doesn't always predict your actual enzyme activity at a given moment.

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The Codeine Example: Why It Matters

Codeine is the clearest illustration of why CYP2D6 status matters — and why the FDA got involved.

Codeine is what pharmacologists call a prodrug. By itself, codeine has very little pain-relieving effect. CYP2D6 converts it into morphine, which is the actual active compound. This sounds simple, but the consequences for people at either metabolizer extreme are serious:

• Poor Metabolizers convert almost no codeine to morphine. They often feel little to no pain relief. They may be labeled as drug-seekers or overstating their pain, when in reality their genetics simply prevent the drug from working.

• Ultrarapid Metabolizers convert codeine to morphine extremely rapidly and at higher concentrations. This can cause life-threatening respiratory depression — especially dangerous in children and in breastfeeding mothers (whose breast milk can carry elevated morphine levels to infants).

Several infant deaths linked to maternal codeine use in UM women led the FDA to issue a Drug Safety Communication in 2017, restricting codeine use in children under 12 and in nursing mothers. Many countries have followed suit.

Tramadol follows a similar pattern. CYP2D6 converts tramadol to its more potent active metabolite, O-desmethyltramadol. Poor Metabolizers may experience inadequate analgesia; Ultrarapid Metabolizers face elevated risk.

This is why pharmacogenomics isn't just academic — it has direct, documented implications for drug safety.

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Understanding CYP2D6 in Your Raw Data

If you've downloaded your raw DNA file, you can search for specific CYP2D6 variants (SNPs). Here are three that appear in consumer chip data and correspond to known star alleles:

Your raw data file will show each rsID with a two-letter genotype (e.g., AA, AG, GG). The minor allele at each position is what you're looking for.

The Critical Limitation You Must Understand

Consumer DNA chips are not designed for reliable CYP2D6 genotyping. This is not a minor caveat — it's fundamental to interpreting anything you find.

Here's why:

1. Copy number variation (CNV): The most clinically meaningful difference between Normal and Ultrarapid Metabolizers is the number of gene copies. Chips measure individual SNPs, not gene duplications or deletions. A person with three functional copies of CYP2D6 (Ultrarapid) and a person with two (Normal) will look identical on a standard SNP chip for the common SNPs listed above.

2. Star allele complexity: CYP2D6 has over 100 recognized star alleles. Consumer chips test a handful of SNPs. Inferring a star allele from one or two positions is like reading one page of a book and summarizing the whole novel.

3. 23andMe's own history: 23andMe has historically not offered a reliable CYP2D6 report in their Health + Ancestry product, precisely because of these technical limitations. The raw data contains individual SNPs, but the company recognizes that converting those into a metabolizer prediction is unreliable with chip data alone.

For a clinically actionable CYP2D6 result, you need a dedicated pharmacogenomic panel — services like GeneSight, Genomind, or a pharmacist-administered PGx panel. These use sequencing or specialized assays that can detect CNVs and rare star alleles that chips miss entirely.

Finding the SNPs in your raw data is still educational — it can tell you whether you carry the *4 allele (rs3892097), for example, which is a strong signal worth discussing with a pharmacist. But it cannot give you a complete metabolizer classification.

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How to Download Your Raw DNA Data

If you haven't already downloaded your file, here's where to find it:

• 23andMe: Account menu → Settings → 23andMe Data → Download Raw Data. You'll receive a .txt file with rsIDs and genotypes. (Note: if you haven't downloaded it yet, the 23andMe bankruptcy situation makes this especially urgent.)
• AncestryDNA: DNA → Settings → Download Raw DNA Data. File format: .txt.
• MyHeritage: DNA → Manage DNA Kits → Download → Raw DNA Data. ZIP file containing a .csv.

All three formats are tab- or comma-separated text files you can open in a text editor, spreadsheet, or terminal.

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Finding CYP2D6 SNPs in Your Raw Data

Once you have your file, searching for specific rsIDs is straightforward.

Text editor (macOS/Windows): Open the file and use Find (Cmd+F or Ctrl+F) to search for rs3892097. The line will show the rsID, chromosome, position, and your two-letter genotype.

Terminal (macOS/Linux):

grep "rs3892097" your_genome_file.txt
grep "rs1065852" your_genome_file.txt

Spreadsheet (Excel/Google Sheets): Import the file as tab-delimited, then use Ctrl+F to search the rsID column.

Once you have your genotypes for these positions, you can ask a tool like Ask My DNA what they mean for your CYP2D6 status — with the understanding that this is a starting point for a conversation, not a clinical result.

You can also run your raw file through third-party interpretation tools. For a comparison of what's available, see our guide to the best DNA upload sites in 2026, or if you've used Promethease, our breakdown of how to read a Promethease report walks through CYP2D6 entries specifically.

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What Your CYP2D6 Result Means (and Doesn't Mean)

What it CAN tell you:

• Whether you carry one of the more common, well-characterized loss-of-function variants (like *4)
• That you have a data point worth raising with a pharmacist before starting a CYP2D6-metabolized drug
• Possible context if you've ever had an unexpected reaction to a medication in the list above

What it CANNOT tell you:

• Your complete CYP2D6 metabolizer status (chip data misses CNVs and most rare alleles)
• How you'll respond to any specific drug — drug interactions, other enzyme pathways, and individual variation all play roles
• Whether you need a dose change — that determination requires a clinical specialist
• Your current functional metabolizer status (phenoconversion from drug interactions can override genetics)

The most useful framing: your raw data CYP2D6 information is a conversation starter, not a diagnosis. If you're starting a new medication that CYP2D6 metabolizes significantly — particularly codeine, tramadol, tamoxifen, or a tricyclic antidepressant — it's worth mentioning to your pharmacist that you've looked at your raw DNA and found [X]. A good pharmacist will know how to factor it in, and may recommend a formal PGx panel if it seems clinically relevant.

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How Testing Platforms Handle CYP2D6

If you want the most clinically reliable CYP2D6 result, a pharmacist-ordered PGx panel or a service like GeneSight is the right path. Consumer chip data is a starting point — useful for curiosity and preliminary awareness, but not a substitute for clinical testing when the stakes are high.

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FAQ

Can my DNA really affect how a painkiller works?

Yes, and this is one of the best-documented examples in pharmacogenomics. Codeine and tramadol are prodrugs that require CYP2D6 to become active. If you're a Poor Metabolizer, these drugs may provide little relief. If you're an Ultrarapid Metabolizer, you may convert them to their active forms faster than expected, which can increase side effect risk. This is why the FDA restricted codeine use in children and nursing mothers after deaths linked to Ultrarapid Metabolizer genetics.

Is 23andMe raw data enough to know my CYP2D6 type?

Not reliably. Consumer chips test a small number of SNPs and cannot detect gene copy number variations (duplications/deletions), which are essential for identifying Ultrarapid and some Poor Metabolizer statuses. You can find individual SNPs like rs3892097 in your raw data — which is informative — but it doesn't give you a complete, clinically accurate metabolizer classification. For that, you need a dedicated pharmacogenomic panel.

*What should I do if I find I carry the 4 allele (rs3892097)?

Finding one copy of *4 means you may be an Intermediate Metabolizer, depending on your other allele (which chip data may not fully characterize). This is worth mentioning to your doctor or pharmacist, particularly if you're being prescribed a CYP2D6-metabolized medication. Don't change or stop any medication on your own — bring the information to a healthcare provider who can put it in clinical context.

Can other medications affect my CYP2D6 status?

Yes. Several drugs are potent CYP2D6 inhibitors — including the antidepressants fluoxetine (Prozac) and paroxetine (Paxil). Taking one of these can effectively make a Normal Metabolizer behave like a Poor Metabolizer for other CYP2D6-processed drugs. This phenomenon is called phenoconversion. It's one reason why your genetic result alone doesn't tell the whole story — your current medication list matters too.

Does ancestry affect which CYP2D6 variants I'm likely to carry?

Yes, significantly. The *4 allele (non-functional) is most common in people of European ancestry — roughly 20–25% carry at least one copy. The *10 allele (reduced function) is much more prevalent in East Asian populations. Ultrarapid Metabolizer duplications are more frequent in North African and Ethiopian populations. This is why ancestry can be a rough predictor of pharmacogenomic risk, though it's never a substitute for actual genotyping.

Does tamoxifen efficacy depend on CYP2D6?

Research suggests it can. Tamoxifen is converted by CYP2D6 into endoxifen, which is its primary active metabolite. Poor Metabolizers produce less endoxifen, and some studies have found associations with reduced treatment efficacy. This is an active area of research, and clinical guidelines from CPIC (Clinical Pharmacogenomics Implementation Consortium) provide nuanced guidance on interpreting this. Women taking tamoxifen who are concerned about CYP2D6 status should discuss clinical PGx testing with their oncologist.

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Conclusion

CYP2D6 is one of the most clinically relevant pharmacogenes in consumer DNA files — it affects responses to antidepressants, pain medications, beta-blockers, and tamoxifen. Your raw data may contain important SNPs like rs3892097 and rs1065852. But chip-based data has real limits for CYP2D6, particularly around gene duplications, and it should be understood as a starting point rather than a diagnostic result.

Curious what your raw DNA file shows for CYP2D6? Upload your genome to Ask My DNA and ask "What CYP2D6 variants do I have?" — your first question is free, no credit card required. Explore your DNA at askmydna.com/en.

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