ABCB1 rs2235040: What Your Genotype Means
The rs2235040 variant is a genetic change located within the ABCB1 gene, which provides instructions for making the P-glycoprotein transporter. This protein acts as a cellular pump, and research suggests this variant may influence how individuals respond to certain medications and experience side effects.
What each genotype means
Typical P-glycoprotein transport
You carry two copies of the common C allele (reported as the G allele on the reverse genomic strand in some research). Clinical evidence evaluating rs2235040 is limited and conflicting; some antidepressant studies suggest common homozygotes may experience differing side effect rates or drug exposure, but meta-analyses have not found conclusive clinical associations. You should not change any medication regimen based on this result and should discuss any dosing or drug choice questions directly with your clinician or pharmacist.
Carried by approximately 70% to 80% of individuals in European and East Asian populations, but less common in South Asian populations where the variant allele is enriched.
Intermediate P-glycoprotein variation
You carry one copy of the T allele (often noted as the A allele on the reverse strand), which has been evaluated for subtle changes in P-glycoprotein drug transport across the blood-brain barrier. Some exploratory studies report differences in remission rates or adverse effects for certain P-glycoprotein substrates like paroxetine, but major pharmacogenomics guidelines currently classify this evidence as limited and inconclusive. Always consult your prescribing doctor or pharmacist before making any decisions regarding your medications.
Carried by roughly 20% to 25% of individuals of European ancestry and present at higher rates in South Asian populations.
Altered P-glycoprotein variation
You carry two copies of the less common T allele (annotated as AA in reverse-strand literature). While individual studies have tentatively linked this genotype to differences in substrate drug exposure and treatment response, robust clinical meta-analyses demonstrate that the overall evidence remains weak and non-definitive. Do not alter any medication dosage or schedule on your own; consult a healthcare provider or clinical pharmacist for personalized guidance.
Carried by roughly 1% to 3% of individuals of European and East Asian descent, but occurs with notably higher prevalence in South Asian populations.
Understanding the rs2235040 Variant
The rs2235040 variant is a single nucleotide polymorphism (SNP) found within the ABCB1 gene, also historically known as the multidrug resistance 1 (MDR1) gene. A SNP represents a variation at a single position in the DNA sequence. In the context of rs2235040, researchers look at whether an individual carries the C or T allele at this specific location. This gene is located on chromosome 7 and is responsible for producing P-glycoprotein, a protein that functions as an ATP-dependent efflux pump. By actively transporting various substances out of cells, this protein plays a critical role in the body's defense against toxins and influences the absorption, distribution, and elimination of many pharmaceutical drugs. Because this variant is located in a gene that governs drug transport, it is a subject of interest in the field of pharmacogenomics, which studies how genetic differences affect individual responses to medications.
The Role of the ABCB1 Gene
The ABCB1 gene encodes P-glycoprotein, a member of the ATP-binding cassette (ABC) transporter family. This protein is expressed in various tissues throughout the body, including the blood-brain barrier, the liver, the kidneys, and the lining of the intestines. Its primary function is to act as a biological gatekeeper, pumping xenobiotics—foreign chemical substances like drugs—out of cells. By limiting the entry of certain compounds into the brain or facilitating their excretion through the liver and kidneys, P-glycoprotein significantly impacts the bioavailability and therapeutic efficacy of many drugs. When the efficiency of this pump is altered by genetic variants, it can lead to differences in how much of a drug reaches its target site or how long it remains in the body. This can potentially result in variations in therapeutic success or the likelihood of experiencing adverse drug reactions.
Research Associations and Evidence Strength
Research into rs2235040 has primarily focused on its association with drug response, particularly in the context of psychiatric medications. Some studies have suggested that this variant may influence remission rates and the frequency of side effects in patients treated with P-glycoprotein substrate drugs, such as certain antidepressants. For instance, some evidence indicates that individuals with specific genotypes may experience different levels of side effects when taking medications like citalopram, fluvoxamine, or paroxetine. However, it is important to note that the evidence strength for these associations is currently considered limited. Many studies are conducted on small cohorts, and results can be mixed or difficult to replicate across different populations. While these findings are scientifically interesting, they do not currently provide a definitive clinical tool for predicting individual drug responses. Further large-scale, well-controlled clinical trials are necessary to fully understand the functional impact of this variant and its potential utility in personalized medicine.
Population Frequency
Genetic studies have observed that the frequency of the rs2235040 variant can vary significantly across different ancestral groups. Research has noted that this variant is particularly enriched in South Asian and Indian sub-populations compared to other global groups. Understanding these population-specific frequencies is a key component of pharmacogenomic research, as it helps scientists identify which groups might be more likely to carry specific genetic profiles. Because allele frequencies differ by ancestry, findings from one population cannot always be generalized to others. Researchers continue to catalog these variations to build a more comprehensive map of human genetic diversity, which is essential for ensuring that future medical insights are applicable and equitable across all global populations.
What You Can Do With This Information
If you have received information about your rs2235040 genotype, it is important to view it as a piece of scientific data rather than a medical diagnosis. Because the evidence linking this variant to specific clinical outcomes is limited and not yet standard practice in clinical care, it should not be used to make independent decisions about your health or medication regimen. You should never start, stop, or change the dosage of any prescribed medication based on genetic test results without consulting your healthcare provider. If you are concerned about how a medication is affecting you, or if you are interested in how your genetics might influence your treatment, bring this information to your doctor or pharmacist. They are the best-equipped professionals to interpret this data in the context of your overall health, medical history, and current treatment plan.
How common is this variant?
The rs2235040 variant shows significant variation in frequency across global populations, with notable enrichment observed in South Asian and Indian sub-populations.
Frequently asked questions
Does the rs2235040 variant mean I will have drug resistance?
No, having this variant does not mean you are resistant to all drugs. It is a genetic marker that may influence the efficiency of a specific protein, but it is only one of many factors that determine how your body processes medications.
Can I use this genotype to choose my antidepressant?
No, you should not use this information to select or change your medication. Genetic testing for this variant is not currently a standard clinical requirement for prescribing antidepressants, and any changes to your treatment must be managed by your doctor.
Is rs2235040 the same as the MDR1 gene?
rs2235040 is a specific genetic variant located within the ABCB1 gene, which is also known as the MDR1 gene. The gene provides the instructions for the protein, while the variant is a specific change in the DNA sequence of that gene.
Where can I find more information about my specific genotype?
You can discuss your genetic report with a qualified healthcare provider or a genetic counselor. They can help you understand the limitations of the current research and how it relates to your specific medical situation.
Sources & further reading
Educational information only, last refreshed 10/18/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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This variant is studied for its influence on the pharmacokinetics of immunosuppressive drugs like cyclosporine and tacrolimus in transplant patients.
Synonymous variant (c.3435C>T) in ABCB1 linked to altered P-glycoprotein expression and multi-drug transporter pharmacokinetics.
Nonsynonymous variant in ABCB1 altering P-glycoprotein transporter kinetics.
A variant associated with potential differences in drug absorption and clinical outcomes in patients undergoing specific pharmacological therapies.
This SNP is linked to variations in the pharmacokinetics of drugs that are substrates for the ABCB1 transporter protein.
Synonymous exon 26 variant in ABCB1 linked to altered mRNA stability and variable response to multiple cardiovascular medications.