SLC22A1 rs72549309: Metformin Transport and Genetics
The rs72549309 polymorphism is a genetic variant in the SLC22A1 gene, which encodes the organic cation transporter 1 (OCT1). This variant causes reduced or impaired uptake of organic cations into liver cells, and it has been studied for its potential effects on glycemic response and gastrointestinal tolerance during metformin therapy. Clinical evidence linking this specific marker to treatment outcomes remains limited and mixed across diverse patient populations.
What each genotype means
Typical OCT1 transporter function
This genotype represents the most common form of the SLC22A1 gene, which encodes the OCT1 transporter responsible for moving metformin into liver cells. Individuals with this genotype typically exhibit standard transporter activity, though clinical response to metformin can still be influenced by other genetic and environmental factors. Please discuss your medication management and any concerns regarding treatment efficacy with your healthcare provider.
This is the most common genotype in most global populations, including those of European ancestry.
Potential reduced transporter activity
This genotype includes one copy of the variant allele, which may be associated with reduced function of the OCT1 transporter protein. Research suggests that variations in this gene can influence how metformin is taken up by the liver, potentially affecting blood glucose control or gastrointestinal tolerance. Because evidence for this specific variant is limited, please consult your clinician or pharmacist regarding your metformin therapy and any side effects you may experience.
Carried by approximately 8% of individuals of European ancestry, based on a minor allele frequency of roughly 0.04.
Likely reduced transporter activity
This genotype consists of two copies of the variant allele, which is associated with impaired function of the OCT1 transporter. Reduced OCT1 activity may alter the way your body processes metformin, potentially impacting its effectiveness in lowering blood glucose or increasing the likelihood of gastrointestinal side effects. As this evidence is limited, please discuss your specific treatment plan and any symptoms with your healthcare provider to ensure your medication regimen is appropriate for you.
This genotype is rare, occurring in approximately 0.16% of individuals of European ancestry.
Genomic Context and the SLC22A1 Gene
The rs72549309 variant is located within the SLC22A1 gene on human chromosome 6. SLC22A1 codes for the organic cation transporter 1 (OCT1), an integral membrane protein predominantly localized to the basolateral surface of hepatocytes in the liver, as well as enterocytes within the digestive tract. OCT1 plays a key physiological role in the active uptake of endogenous amines, basic metabolites, and various therapeutic compounds from the circulation into target tissues. The rs72549309 variant results in a coding alteration that disrupts the normal conformation of the transporter pore, leading to a loss or reduction of its transport capabilities compared to the standard wild-type protein.
Biological Mechanisms and Metformin Processing
Metformin is a primary first-line pharmacotherapy for managing blood glucose in individuals with type 2 diabetes mellitus. Because metformin is hydrophilic and exists as a positively charged cation at physiological pH, it relies heavily on specialized transport proteins like OCT1 to cross cellular membranes into hepatocytes, where it exerts its glucose-lowering effects by activating AMP-activated protein kinase (AMPK) and decreasing hepatic gluconeogenesis. When OCT1 function is impaired by genetic variations such as rs72549309, cellular entry of the drug into hepatocytes can be attenuated, leading to altered systemic clearance, higher circulating concentrations, or localized retention in intestinal tissues.
Clinical Evidence: Efficacy and Gastrointestinal Side Effects
Studies evaluating rs72549309 have examined whether individuals carrying the reduced-function allele experience differing glycemic benefits or higher rates of side effects. Reduced hepatic uptake has been hypothesized to blunt the drug's effectiveness in lowering hemoglobin A1c (HbA1c). Concurrently, reduced transport out of the intestinal lumen can lead to local drug accumulation, potentially increasing the risk of adverse gastrointestinal symptoms such as nausea, abdominal cramping, or diarrhea. However, clinical evidence remains classified as limited; several replication cohorts and meta-analyses have observed inconsistent results, suggesting that environmental factors, diet, and variations in related transporters such as OCT2 (SLC22A2) and MATE1 (SLC47A1) also shape clinical outcomes.
How to Interpret Your Genetic Data
While discovering an SLC22A1 rs72549309 variant in personal genomic data offers an interesting biological perspective, it does not constitute a clinical diagnosis or a direct prediction of treatment failure. Pharmacogenomic interactions are complex, and current clinical practice guidelines do not recommend altering diabetes therapy solely on the basis of a single SLC22A1 polymorphism. Anyone currently taking or considering metformin should never stop, start, or modify medication dosages independently. If you experience adverse side effects or suboptimal glycemic control, discuss these symptoms with your physician or pharmacist, who can holistically evaluate therapy options.
How common is this variant?
The rs72549309 variant is relatively uncommon across global populations, with an estimated minor allele frequency of approximately 0.04 in European ancestries and substantially lower frequencies or near-absence in many East Asian and African cohorts.
Frequently asked questions
Does carrying the rs72549309 variant mean metformin will not work for me?
No, having one or two copies of this variant does not mean metformin will fail. While studies show the variant can decrease OCT1 transporter efficiency in cellular models, real-world clinical response depends on multiple genes, lifestyle, and dosage. Many people with reduced-function variants still achieve adequate glycemic control.
Can rs72549309 explain stomach upset or diarrhea from metformin?
Research suggests that reduced-function OCT1 variants may impair the clearance of metformin from intestinal tissues, which could contribute to gastrointestinal side effects. However, gastrointestinal discomfort is very common when starting metformin regardless of genetics, so you should speak with your doctor about potential adjustments such as extended-release formulations.
Should my doctor change my diabetes medication based on this genetic test?
No, professional clinical guidelines do not currently recommend changing metformin dosing or choosing alternative drugs based solely on SLC22A1 genotype testing. Clinical decisions are guided by your actual blood glucose levels, HbA1c tests, and your personal tolerance of the medication.
What other genes interact with SLC22A1 during metformin treatment?
Metformin movement through the body involves several transporters, notably OCT2 (encoded by SLC22A2) in the kidneys and MATE1/MATE2 (encoded by SLC47A1 and SLC47A2), which manage renal excretion. Genetic variations across these complementary transporters can influence overall drug levels and bodily response.
Sources & further reading
Educational information only, last refreshed 9/9/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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Functional non-synonymous variant (M420del) in the organic cation transporter OCT1, significantly impacting the hepatic uptake of various drugs including metformin.
An intronic variant in the organic cation transporter gene associated with altered metformin side-effect profiles.
A variant associated with the occurrence of gastrointestinal side effects in metformin users.
Variant in SLC22A1 (OCT1) associated with altered metformin transport and glycemic response.
Also known as OCT1 p.Met420del, this loss-of-function deletion diminishes hepatic uptake and glycemic response to metformin in patients with type 2 diabetes.
A well-characterized loss-of-function variant (M420del) in the organic cation transporter 1 (OCT1) that reduces hepatic uptake of metformin and other basic drugs, modulating therapeutic efficacy and side effects.