Is Chlorpheniramine, Codeine and Phenylephrine affected by genetics?
Partially. 1 of 3 ingredients has pharmacogenetic evidence.
Chlorpheniramine, codeine and phenylephrine contains 3 active ingredients, and 1 of them has published pharmacogenetic guidelines. The relevant gene is CYP2D6. Your genotype can change how that ingredient behaves in your body, while the other ingredients aren't affected by genetics in any clinically established way. The strongest evidence level on this page is Strong, from the published guidelines shown below.
Pharmacogenetic guidelines are written for one ingredient at a time, so the guidance below is for each ingredient on its own. What your genes mean for a combination product is less clear, because the dose and the other ingredients can change things. If you take Chlorpheniramine, codeine and phenylephrine, it's worth talking over with your prescriber or pharmacist. How we handle combination products.
What's in Chlorpheniramine, codeine and phenylephrine
Chlorpheniramine No known pharmacogenetics
No strong published pharmacogenetic guideline currently applies to chlorpheniramine.
Codeine Affected by CYP2D6
Affected by CYP2D6. Guidance from CPIC, FDA, strong evidence.
Read the full codeine genetics guidePhenylephrine No known pharmacogenetics
No strong published pharmacogenetic guideline currently applies to phenylephrine.
Codeine phenotype recommendations
Published guidance from CPIC and FDA on how codeine should be dosed or substituted based on your CYP2D6 phenotype.
| Phenotype | What it means | Recommendation | Evidence |
|---|---|---|---|
| Ultrarapid MetabolizerCYP2D6 | Your body turns codeine into morphine too fast, which can cause dangerous side effects. A different pain reliever is usually suggested. | CPIC Avoid codeine use because of potential for serious toxicity. If opioid use is warranted, consider a non-tramadol opioid. FDA Codeine is contraindicated in children under 12 years. Refer to FDA labeling, which warns of life-threatening respiratory depression in ultrarapid metabolizers. |
Strong |
| Normal MetabolizerCYP2D6 | Your body processes codeine normally, so the usual dose should work as expected. | CPIC Use codeine label recommended age- or weight-specific dosing. FDA Initiate therapy with recommended starting dose. |
Strong |
| Intermediate MetabolizerCYP2D6 | Your body turns codeine into its active form more slowly. The usual dose is used. If it doesn't ease your pain, your doctor may try another pain reliever. | CPIC Use codeine label recommended age- or weight-specific dosing. If no response and opioid use is warranted, consider a non-tramadol opioid. FDA Initiate therapy with recommended starting dose. |
Moderate |
| Poor MetabolizerCYP2D6 | Your body turns very little codeine into its active form, so it likely won't ease your pain. A different pain reliever is usually suggested. | CPIC Avoid codeine use because of possibility of diminished analgesia. If opioid use is warranted, consider a non-tramadol opioid. FDA No specific dosing change; codeine may be less effective. Refer to FDA labeling. |
Strong |
| IndeterminateCYP2D6 | The impact of your genotype on response to this drug is unknown. | CPIC + FDA Initiate therapy with recommended starting dose. |
Not rated |
| Not availableCYP2D6 | The impact of your genotype on response to this drug is unknown. | CPIC + FDA Initiate therapy with recommended starting dose. |
Not rated |
The gene behind the guidance
CYP2D6 Cytochrome P450 2D6
CYP2D6 is the most clinically important pharmacogene. It metabolizes around a quarter of all prescription drugs, including many antidepressants, opioids, and stimulants. The gene is unusually variable: roughly 7 percent of people are poor metabolizers (they barely activate CYP2D6), and another 1 to 3 percent are ultrarapid metabolizers (their enzyme is overactive).
The v4 report preserves the activity score used in its interpretation. Some medicines use a combined CYP2D6/CYP2C19 recommendation. CYP2D6 inhibitors can change functional metabolism; a genotype alone does not capture that effect.
See all drugs affected by CYP2D6Browse the full drug class: Pain medications.
Related medications
Find out how your genetics affect Chlorpheniramine, codeine and phenylephrine
Informational only, not medical advice. Pharmacogenetic guidance describes population-level patterns; your individual response depends on many factors. Never start, stop, or change a medication without talking to your prescribing clinician.