Some people’s bodies clear certain medicines so quickly that a standard dose never builds up enough to work. The usual clue is a pattern of medicines that disappoint, but a pattern alone can’t prove anything, because many things make a medicine fail. The most direct way to know is a gene test for medicines, which reads how your drug-processing enzymes are built. And being fast isn’t always bad news: for some medicines it means stronger effects, not weaker ones.1Synlab. What is pharmacogenetics and how it influences medication decisions
Signs Your Body May Clear Medicine Too Quickly
The main sign is a medicine that just doesn’t work. When your body breaks a drug down very fast, it can be cleared before it has time to relieve symptoms.2GeneSight. How Your Genes Affect Medication Success Standard doses are set for people with average drug processing,3SelfDecode. Your Medications Aren’t Working. Your Genes May Be Metabolizing Them Too Fast so a dose that helps most people can leave you with too little in your blood to feel any benefit.4Genomind. What Everyone Needs to Know About Drug Metabolism
Fast processors may tolerate some drugs unusually well. In a study of about 9,500 people taking antidepressants, those who processed them quickly through one enzyme were less likely to quit because of side effects.5PubMed Central. Impact of CYP2C19 metaboliser status on SSRI response: a retrospective study of 9500 participants of the Australian Genetics of Depression Study So little benefit alongside few side effects can fit the fast-processing pattern, though it is not proof.
Plenty of other things make a medicine seem useless. Missed or irregular doses are the most common reason. The diagnosis may be wrong, or the drug may simply not suit that condition. And some medicines take weeks to show any effect, so early judgement misleads.
That timing matters for telling a failing drug from a slow starter. Many antidepressants need several weeks at a steady dose before the full benefit shows, so a drug that feels useless in the first week or two hasn’t had a fair trial. A fast processor’s pattern is different: even after a proper trial at a well-taken dose, nothing much changes, and raising the dose brings little more. Pain relievers are easier to judge, because relief should show within hours. If it wears off far sooner than the label suggests, that is a more telling clue.
A log makes all of this visible. Record the date, dose and time you took each dose, which shows whether any were missed. Add a daily rating of the symptom being treated, such as pain or mood from 1 to 10, and note side effects, including having none. Write down the start date and every dose change too, so you and your doctor can see whether the trial was long enough. A few weeks of notes gives a doctor far more to work with than a general memory that nothing helped. Without knowing your profile, ineffective doses tend to get blamed on the drug rather than on how fast you break it down.6SelfDecode. How to Know If You Metabolize Medication Too Fast7SelfDecode. How to Know If You Metabolize Medication Too Fast
Why Some People Are Born Fast Metabolizers
A family of liver enzymes known as CYP is a major route by which many drugs are broken down.8Frontiers in Pharmacology. Physiologic and pharmacokinetic changes in pregnancy One of them, CYP2D6, handles many antidepressants and pain medicines. Its speed varies widely because more than 100 known differences in the CYP2D6 gene produce enzymes ranging from inactive to overactive.9St. Jude Children’s Research Hospital. Cytochrome P450 2D6 (CYP2D6)
People with several copies of the CYP2D6 gene have more enzyme activity than normal and are called ultrarapid metabolizers.10St. Jude Children’s Research Hospital. Cytochrome P450 2D6 (CYP2D6) About 3 in 100 people are ultrarapid metabolizers for this enzyme.11St. Jude Children’s Research Hospital. Cytochrome P450 2D6 (CYP2D6) The more working copies you carry, the faster you process drugs, and one family carried 12 copies.12PubMed. Inherited amplification of an active gene in the cytochrome P450 CYP2D locus as a cause of ultrarapid metabolism of debrisoquine Because the genes are inherited, fast metabolism can run in families.
On a test report, people are sorted into categories. Poor metabolizers have little enzyme activity, and intermediate metabolizers fall between poor and normal. Normal metabolizers match the doses drugs are designed around. Rapid and ultrarapid sit above normal, with ultrarapid usually coming from extra gene copies.
These gene differences depend strongly on ancestry, so how common fast processing is varies between populations.13PubMed Central / Elsevier. Cytochrome P450 enzymes in drug metabolism: regulation of gene expression, enzyme activities, and impact of genetic variation Doses, though, are often prescribed the same way across different groups.14SpringerLink / PubMed Central. Ethnic differences in drug disposition and responsiveness Other enzymes, such as CYP2C19, have their own fast versions, so you can be fast for one enzyme and normal for another.15PubMed Central. Impact of CYP2C19 metaboliser status on SSRI response: a retrospective study of 9500 participants of the Australian Genetics of Depression Study
The Test That Tells You for Sure
A pharmacogenetic test, or gene test for medicines, looks at the genes for your drug-processing enzymes.16The Jackson Laboratory. Pharmacogenomic test report nomenclature & terminology Good tests check for extra gene copies, which is what makes someone an ultrarapid metabolizer for CYP2D6.17PubMed Central. The genetic landscape of major drug metabolizing cytochrome P450 genes—an updated analysis of population-scale sequencing data Among 202 psychiatric patients tested, about 3.5 in 100 carried duplicated CYP2D6 genes.18Clinical Chemistry. Ultrarapid drug metabolism: PCR-based detection of CYP2D6 gene duplication
Reports list your gene pair, one version from each parent, and what it means for how the enzyme works.19The Jackson Laboratory. Pharmacogenomic test report nomenclature & terminology Results are often given as dosing notes for specific drugs.20The Jackson Laboratory. Pharmacogenomic test report nomenclature & terminology Standard labels like “ultrarapid metabolizer” are meant to make results read the same everywhere.21Genetics in Medicine. Standardizing terms for clinical pharmacogenetic test results: consensus terms from the Clinical Pharmacogenetics Implementation Consortium (CPIC)
Getting tested is simple. Most tests use a cheek swab or a blood sample. Your doctor or a psychiatrist can order one, and consumer kits also exist. Results usually take days to a few weeks, and since your genes don’t change, one test serves for life.
A blood test of the drug itself is another clue. It can show a level far below expected despite steady dosing.22PubMed. Managing rapid metabolizers of antidepressants In one person with three working CYP2D6 genes, the antidepressant paroxetine couldn’t be detected in the blood at all.23PubMed. CYP2D6 inhibition by selective serotonin reuptake inhibitors: analysis of achievable steady-state plasma concentrations and the effect of ultrarapid metabolism at CYP2D6
A gene test has limits. It doesn’t capture the effects of diet, smoking or other drugs you take. It can’t guarantee a drug will work, only how fast it may be processed. Consumer reports should be reviewed with a doctor before any dose changes.
Useful questions for your doctor: Which enzymes were tested, and were gene copies counted? Do my current medicines use those enzymes? Would a drug blood level help confirm the result?
Which Medicines Fast Metabolism Affects
Antidepressants are the best-known example. People who process them fast may not respond even to high doses because blood levels stay too low.24PubMed. Managing rapid metabolizers of antidepressants Simply raising doses of older antidepressants very high risks building up harmful breakdown products.25PubMed. Managing rapid metabolizers of antidepressants
Prodrugs work the opposite way. A prodrug is a medicine your body has to activate, so fast processing makes more of the active form, raising side-effect risk.26Synlab. What is pharmacogenetics and how it influences medication decisions The painkiller codeine is changed into morphine by CYP2D6. Ultrarapid metabolizers had about 50% higher morphine levels after codeine,27PubMed. Pharmacokinetics of codeine and its metabolite morphine in ultra-rapid metabolizers due to CYP2D6 duplication which means they can have exaggerated and potentially dangerous opioid effects.28PubMed. Pharmacokinetics of codeine and its metabolite morphine in ultra-rapid metabolizers due to CYP2D6 duplication If you are ultrarapid for CYP2D6, tell any prescriber before taking codeine.
The same gene result can therefore call for a higher dose of one drug and a lower dose of another. A pharmacist can tell you which kind each of your medicines is.
Fast for one enzyme isn’t fast for everything. Each medicine depends on particular enzymes, so being fast for CYP2D6 matters only for drugs that rely on it.29PubMed Central / Elsevier. Cytochrome P450 enzymes in drug metabolism: regulation of gene expression, enzyme activities, and impact of genetic variation Some drugs use non-CYP enzymes entirely.30WIREs Computational Molecular Science. Recent advances in the prediction of non‐CYP450‐mediated drug metabolism
Things Besides Genes That Speed Up Drug Clearance
Smoking, charcoal-grilled food and cruciferous vegetables like broccoli and cabbage speed up breakdown of many substances.31PubMed. Influence of diet and nutritional status on drug metabolism Switching to a high-protein, low-carbohydrate diet raised clearance of the blood-pressure drug propranolol by 74%.32PubMed Central. The Impact of Diet and Exercise on Drug Responses Grapefruit juice works the other way, slowing breakdown and raising levels of some heart drugs.33PubMed. Influence of diet and nutritional status on drug metabolism
Some drugs boost enzyme activity, which can weaken other medicines you take.34Genomind. What Everyone Needs to Know About Drug Metabolism Give your doctor a list of every prescription, supplement and over-the-counter product you use.
In pregnancy, activity of the enzyme CYP3A4 rises, so some drugs are cleared faster and doses may need adjusting.35Frontiers in Pharmacology. Physiologic and pharmacokinetic changes in pregnancy The epilepsy drug lamotrigine is cleared faster in pregnancy.36Frontiers in Pharmacology. Physiologic and pharmacokinetic changes in pregnancy In children, enzymes are still developing, so drug handling changes with age.37PubMed. Meta-analysis of hepatic cytochrome P450 ontogeny to underwrite the prediction of pediatric pharmacokinetics using physiologically based pharmacokinetic modeling If a medicine seems to lose its effect, tell your doctor about any change in smoking, diet or new prescriptions.
What to Do If You Are a Fast Metabolizer
Ultrarapid metabolizers may need higher doses of regular medicines for a full effect.38PubMed Central. Pharmacogenetic Testing: A Tool for Personalized Drug Therapy Optimization One psychiatric guide suggests target doses 135 to 180% higher, raised faster but slowed if side effects appear.39Psychopharmacology Institute. Pharmacogenetics-Guided Dosing: Strategies for Poor and Rapid Metabolizers For prodrugs, a lower dose or different drug is advised.40Synlab. What is pharmacogenetics and how it influences medication decisions Never raise a dose on your own.
Another option is slowing the enzyme. In 12 fast processors whose antidepressant wasn’t working, adding fluoxetine or paroxetine, which block CYP2D6, brought levels into range in 10.41PubMed. Managing rapid metabolizers of antidepressants Seven of those 10 had good lasting responses, and the combination was well tolerated.42PubMed. Managing rapid metabolizers of antidepressants
Once you have results, keep a copy of your report and add it to your medical records. Tell pharmacists and new doctors your metabolizer type, and ask about it before surgery or new pain prescriptions. Even a medicine that seems useless should be discussed with your doctor before you stop it.