Summary

CYP2D6 rs3892097 tags the *4 loss-of-function allele — the most common cause of poor CYP2D6 metabolism in Europeans — which renders codeine ineffective, reduces tramadol and tamoxifen efficacy, and alters clearance of ~25% of all prescribed drugs including many antidepressants, beta-blockers, and antipsychotics.

Genotype spectrum

GG (normal, *1/*1 at this locus)

Standard drug metabolism. Prescribed drugs work as their clinical trials predicted.

GA (intermediate, *1/*4)

Partial function is often clinically sufficient. Most GA carriers notice no issues with standard prescriptions.

AA (poor metaboliser, *4/*4)

Knowing this BEFORE you're prescribed an affected drug prevents treatment failure and adverse effects. This is one of the highest-leverage pharmacogenomic findings — directly actionable at point of prescribing.

Practical takeaway

For All Carriers

This is a medical reference, not a lifestyle recommendation. The primary action is informational: ensure your CYP2D6 status is in your medical record and communicated to prescribers.
For AA Carriers (Poor Metabolisers)
• Codeine: Will not provide adequate analgesia. Request alternative opioids (oxycodone, morphine — these do not require CYP2D6 activation) or non-opioid analgesics.
• Tramadol: Markedly reduced efficacy. Same alternatives apply.
• Tamoxifen: Discuss with oncologist. Endoxifen level monitoring or aromatase inhibitor alternatives per CPIC guidelines.
• Antidepressants: If starting an SSRI, consider those less dependent on CYP2D6 (sertraline, citalopram/escitalopram have alternative clearance pathways). If prescribed a CYP2D6-primary antidepressant (fluoxetine, paroxetine), expect dose reductions per CPIC tables.
• Beta-blockers: Metoprolol is a CYP2D6 substrate — poor metabolisers may experience exaggerated effects at standard doses.
For GA Carriers (Intermediate)
• Most standard prescriptions will work adequately.
• Mention CYP2D6 intermediate status if codeine analgesia is insufficient, or if side effects seem disproportionate on a new CYP2D6 substrate.

Expected response window: N/A — CYP2D6 status is a fixed metabolic parameter. It applies whenever an affected drug is prescribed.

Evidence detail

What This Gene Does

CYP2D6 is a cytochrome P450 liver enzyme responsible for metabolising approximately 25% of all clinically used drugs. For pro-drugs like codeine and tramadol, CYP2D6 is required to convert the inactive parent compound into its active metabolite — without functional CYP2D6, these drugs simply do not work. For other substrates (many SSRIs, SNRIs, beta-blockers, antipsychotics), CYP2D6 is the primary clearance pathway — impaired function causes drug accumulation and increased side-effect risk.

The rs3892097 variant (G>A) introduces a splice-site defect that produces a non-functional protein (CYP2D6*4). This is the most commonly tested pharmacogenomic variant and the most frequent cause of CYP2D6 poor metaboliser status in European-ancestry populations.

Mechanism

CYP2D6 sits in the endoplasmic reticulum of hepatocytes and catalyses oxidative metabolism of substrates via the cytochrome P450 monooxygenase system. The rs3892097 G>A variant disrupts a splice site in intron 3, producing aberrant mRNA that yields no functional protein. Homozygous carriers (AA, 4/4) have effectively zero CYP2D6 enzyme activity.

Pro-drug activation failure: Codeine requires CYP2D6 O-demethylation to become morphine. Without this step, codeine has minimal analgesic effect (only weak parent-compound activity). Tramadol similarly requires CYP2D6 to form its active O-desmethyltramadol metabolite.

Drug accumulation: For substrates where CYP2D6 is the clearance pathway (many SSRIs, tricyclics, beta-blockers, antipsychotics), poor metabolisers experience higher plasma concentrations at standard doses — increasing both therapeutic effect and side-effect risk.

CYP2D6

Summary

Genotype spectrum

Practical takeaway

Evidence detail

Sources (6)