Pain Medications · Tylenol 3, Ultram, Celebrex, Advil

Pain Medication Not Working? Why Your Body May Process It Differently

Two genes account for a large share of unexplained pain medication failures: CYP2D6 determines whether prodrug opioids like codeine and tramadol ever get activated, and CYP2C9 determines how long NSAIDs linger in your system.

Reviewed by the Gene2Rx team · Updated 2026-05-28

Few things are more frustrating than being in pain and having the medication not touch it. The instinct is to assume you need a stronger dose or a different drug. Sometimes that is right. Often it is not. Your genetics play a real part in how well each class of pain medication works for you, and the genes that matter most here are CYP2D6 and CYP2C9.

Important: Seek emergency care if you have difficulty breathing, extreme drowsiness, confusion, or loss of consciousness after taking any opioid pain medication. If you have severe stomach pain, vomiting blood, or black tarry stools while taking NSAIDs, seek immediate medical attention; these can be signs of GI bleeding.

Common reasons pain medication does not work

Wrong pain medication for the pain type

Different types of pain respond to different medications. Inflammatory pain (arthritis, injuries) responds best to NSAIDs like ibuprofen and celecoxib. Nociceptive pain (acute injuries, surgical pain) often responds to opioids. Neuropathic pain (nerve damage, diabetic neuropathy) often does not respond well to either and may need gabapentin, pregabalin, or certain antidepressants.

Underdosing or wrong timing

Many people take pain medication at doses too low to be effective, or wait too long between doses, so pain breaks through before the next dose. Taking pain medication on a schedule (before pain becomes severe) often works better than waiting until you are in serious pain.

Drug tolerance

With opioid medications, your body can develop tolerance over time, so higher doses are needed for the same effect. This is a normal physiological response, not the same as addiction, but it does mean that a dose that once worked can stop being enough.

Underlying conditions

Chronic pain conditions like fibromyalgia, central sensitization, and some autoimmune disorders involve altered pain processing in the brain and nervous system. These conditions usually need a multimodal treatment plan rather than a single pain medication.

If you are a CYP2D6 poor metabolizer, codeine and tramadol are essentially ineffective for you. No dose adjustment will fix this because the activation step is missing.

How your genetics can play a role

Your genetics affect pain medication response through two main mechanisms: how your body activates prodrug opioids (CYP2D6) and how your body processes NSAIDs (CYP2C9). Knowing both can help explain why some pain medications work for you while others do not.

Gene	What it affects
CYP2D6	CYP2D6 activates codeine (converting it to morphine) and tramadol (converting it to O-desmethyltramadol).^[1] Poor metabolizers of CYP2D6 (5-10% of Caucasians) get almost no pain relief from these drugs because the drugs cannot be converted to their active forms. Ultrarapid metabolizers face the opposite risk: conversion happens so fast it can cause dangerous side effects, including respiratory depression.^[2]
CYP2C9	CYP2C9 metabolizes NSAIDs like ibuprofen, celecoxib, meloxicam, and piroxicam.^[3] About 14% of people carry variants that slow this metabolism, which leads to higher drug levels and a higher risk of GI bleeding, kidney problems, and cardiovascular side effects. For these people, lower NSAID doses or alternative pain medications may be safer.

Gene

What it affects

CYP2D6

CYP2D6 activates codeine (converting it to morphine) and tramadol (converting it to O-desmethyltramadol).^[1] Poor metabolizers of CYP2D6 (5-10% of Caucasians) get almost no pain relief from these drugs because the drugs cannot be converted to their active forms. Ultrarapid metabolizers face the opposite risk: conversion happens so fast it can cause dangerous side effects, including respiratory depression.^[2]

CYP2C9

CYP2C9 metabolizes NSAIDs like ibuprofen, celecoxib, meloxicam, and piroxicam.^[3] About 14% of people carry variants that slow this metabolism, which leads to higher drug levels and a higher risk of GI bleeding, kidney problems, and cardiovascular side effects. For these people, lower NSAID doses or alternative pain medications may be safer.

If you are a CYP2D6 poor metabolizer, codeine and tramadol are essentially ineffective for you. No dose adjustment will fix this because the activation step is missing. You need a pain medication that works through a different pathway. If you carry CYP2C9 variants, NSAIDs may last longer in your body than expected, which can cause more side effects at standard doses. Knowing both your CYP2D6 and CYP2C9 status gives your doctor a much clearer picture of which pain medications will work safely for you.

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When to consider pharmacogenetic testing

Pharmacogenetic testing for pain management is worth doing if you have tried multiple pain medications without enough relief, if you have had unexpected side effects from pain medications, or if you are about to undergo surgery and want your post-operative pain management plan tuned to your genetics.

What you can do next

Describe your pain in detail to your doctor: type (sharp, burning, aching), location, triggers, and what makes it better or worse.
Ask about pharmacogenetic testing for CYP2D6 and CYP2C9 status before cycling through more pain medications by trial and error.
Keep a pain diary tracking medication timing, doses, and pain levels so your doctor has real data to work with.
Ask your doctor about multimodal pain management. Combining different approaches (medication, physical therapy, nerve blocks) often works better than relying on a single drug.

Frequently asked questions

Why do some pain medications work for other people but not for me?

Genetic variations in liver enzymes like CYP2D6 and CYP2C9 mean that two people taking the same pain medication at the same dose can have very different drug levels in their bodies. This is one of the main reasons the same medication can work for one person and do nothing for another.

If codeine and tramadol do not work, what opioid alternatives exist?

Morphine, oxycodone, and hydromorphone work through different metabolic pathways and do not depend on CYP2D6 for activation. All opioids carry risks and should only be used under medical supervision. Non-opioid alternatives like gabapentin, certain antidepressants, and regional anesthesia may also help depending on your pain type.

Should I ask for a 'stronger' pain medication if mine is not working?

Not necessarily. The issue may not be strength but how your body processes the medication. A pharmacogenetic test can show whether you need a different class of medication rather than a higher dose of the same one. This approach is safer and often works better.

References

CPIC. CPIC Guideline for Opioids (Codeine, Tramadol) and CYP2D6, OPRM1, and COMT (2021). cpicpgx.org
U.S. Food and Drug Administration. Table of Pharmacogenomic Biomarkers in Drug Labeling (2024). fda.gov
Clinical Pharmacogenetics Implementation Consortium (CPIC). CPIC Guidelines. cpicpgx.org

Disclaimer: This content is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult your healthcare provider before making changes to your medication. Never stop or change a medication without medical supervision.

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