SLCO1B1 decreased function is one of the most common findings on a pharmacogenomic report, and it matters most if you take, or may soon take, a statin. Here is what the result means, how it relates to muscle side effects and what to discuss with your prescriber.
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The SLCO1B1 gene encodes the organic anion (group of compounds that include fatty acids, bile acids, and anionic drugs) transporting polypeptide 1B1 (OATP1B1), a liver-specific transmembrane transporter responsible for the sodium-independent uptake of various endogenous compounds (growing or originating from within an organism), including bilirubin, 17-beta-glucuronosyl estradiol, and leukotriene C4. Additionally, OATP1B1 plays a crucial role in the hepatic clearance (the rate at which the liver removes a substance from the blood) of several drug compounds, such as statins (known to lower LDL cholesterol levels in the blood), bromosulfophthalein (used to measure liver function), and rifampin (used to treat bacterial infections), by facilitating their transport from the bloodstream into hepatocytes for metabolism and excretion.
SLCO1B1 decreased function can impair transporter activity, affecting drug pharmacokinetics (how the body processes a drug) and increasing the risk of adverse drug reactions. The FDA has also specified a few drugs that may result in higher concentrations in people with decreased or poor SLCO1B1 function. We have added two of the highlighted drugs, Atorvastatin (Lipitor), which belongs to the statin class of drugs, and Elagolix (Orilissa), which is a gonadotropin-releasing hormone (GnRH) antagonist used to treat moderate to severe pain caused by endometriosis.
Implications of Decreased SLCO1B1 Function
Genetic variations in SLCO1B1 can result in decreased transporter activity, leading to altered drug handling and increased susceptibility to adverse effects. Decreased SLCO1B1 function is fairly common, and a smaller group of people have poor function, which can slow how quickly the liver takes up and clears some drugs.
Impact of Statins
Statins, commonly prescribed for lowering cholesterol levels, are significantly affected by SLCO1B1 activity. Reduced function of OATP1B1 can lead to higher plasma concentrations of statins, increasing the risk of statin-induced myopathy. For instance, individuals with certain SLCO1B1 polymorphisms can have a noticeably larger area under the plasma-time curve (AUC) for some statins, especially simvastatin, indicating higher systemic exposure.
Impact on Other Medications
Beyond statins, decreased SLCO1B1 function can influence the pharmacokinetics of various drugs across different therapeutic areas:
- Antidiabetic Drugs: Polymorphisms in SLCO1B1 may affect the transport and efficacy of certain oral antidiabetic medications, such as Repaglinide (Prandin), potentially altering therapeutic outcomes.
- Anticoagulants: Some studies have looked at whether SLCO1B1 polymorphisms change blood levels of Edoxaban, an anticoagulant, although the evidence is limited and it is not used to guide dosing.
- Immunosuppressants: Research has shown that SLCO1B1 polymorphisms can significantly influence the pharmacokinetics of mycophenolic acid glucuronide in renal transplant recipients, potentially impacting drug efficacy and safety. By contrast, Tacrolimus (Prograf) levels depend mainly on a different gene, CYP3A5, rather than SLCO1B1.
Pharmacogenomic Testing and RPh LABS
Pharmacogenomic testing offers valuable insights into an individual’s genetic profile, particularly concerning genes like SLCO1B1. By identifying specific polymorphisms, healthcare providers can predict how a patient may respond to certain medications, allowing for personalized drug selection and dosing. This approach minimizes the risk of adverse reactions and enhances therapeutic efficacy.
RPh Labs provides a non-invasive, at-home pharmacogenomic testing kit that requires only a simple cheek swab. This convenient method enables individuals to gain insights into their genetic predispositions affecting drug metabolism. The results can guide healthcare providers in tailoring medication choices and dosages to align with the patient’s unique genetic makeup, optimizing treatment outcomes.
What SLCO1B1 decreased function means on your report
Your SLCO1B1 result describes a transporter, not an enzyme. The SLCO1B1 gene makes OATP1B1, a transporter that pulls statins and some other drugs from the blood into the liver. The liver is where statins do their cholesterol-lowering work, so a slower transporter leaves more statin circulating in the blood and in muscle tissue.
Because SLCO1B1 is a transporter, reports describe it with function labels rather than metabolizer labels. Under current CPIC guidelines the groups are increased function, normal function, possible decreased function, decreased function and poor function.
The best-known variant is c.521T>C, also listed as rs4149056. It is part of several star alleles, including *5 and *15. Carrying one copy of a reduced-function allele usually leads to a result of SLCO1B1 decreased function. You can read more about the gene at MedlinePlus.
Your SLCO1B1 genotype is inherited and never changes, so one test gives you a result you can use for life.
SLCO1B1 poor function vs decreased function
SLCO1B1 poor function means both copies of the gene carry reduced or no-function versions. Transport into the liver is the slowest of all groups, so statin blood levels tend to be highest. SLCO1B1 decreased function means one copy is affected, so the effect is in between.
- Normal function: expected statin levels; usual dosing applies.
- Decreased function: higher statin levels; some statins may need a lower dose limit or an alternative.
- SLCO1B1 poor function: the highest statin levels; guidelines suggest avoiding some statins and limiting doses of others.
- Possible decreased function: used for some mixed combinations, such as one reduced-function copy and one increased-function copy; your prescriber interprets it with other factors.
The label does not mean you will have side effects. Many people with SLCO1B1 decreased function take statins without trouble. The result simply shifts the odds and helps your prescriber pick the statin and dose that give you the best balance of benefit and safety.
Simvastatin and SLCO1B1: the strongest link
Of all statins, simvastatin is the most affected by this gene. Research on simvastatin and SLCO1B1 has shown that people carrying reduced-function variants have higher simvastatin acid levels and a higher risk of muscle problems, especially at high doses.
Current CPIC guidance for simvastatin and SLCO1B1 suggests:
- Decreased or possible decreased function: consider an alternative statin based on the cholesterol lowering you need. If simvastatin is still the best choice, keep the dose below 20 mg a day.
- Poor function: consider an alternative statin.
Separately, the FDA already limits the 80 mg simvastatin dose for everyone because of muscle injury risk. Your SLCO1B1 result adds a personal layer to that general caution.
If you currently take simvastatin, do not stop or change it on your own. Statins lower the risk of heart attack and stroke. Bring your result to your prescriber, who can decide whether to keep your current plan or switch.
Other statins and the genes that affect them
SLCO1B1 affects most statins to some degree, but the size of the effect differs. CPIC guidance covers atorvastatin, fluvastatin, lovastatin, pitavastatin, pravastatin, rosuvastatin and simvastatin, with advice that varies by drug and by how reduced your function is. For several of them the suggestion is a dose limit rather than a switch.
Two other genes on many PGx panels also matter for statins:
- ABCG2 affects rosuvastatin. Reduced ABCG2 function raises rosuvastatin levels, so a lower starting dose may be considered.
- CYP2C9 affects fluvastatin, which relies on this enzyme to be cleared.
Because the genes combine, it helps to have all three tested together. The RPh Labs panel includes SLCO1B1, ABCG2 and CYP2C9, and our medication list shows every statin alongside the genes that affect it.
Recognizing statin muscle pain and statin myopathy
Statin muscle pain usually feels like aching, cramping, tenderness or weakness in large muscles such as the thighs, calves, hips, shoulders or back. It is often on both sides of the body and may start within weeks to months of beginning a statin or raising the dose.
Statin myopathy is the broader term for statin-related muscle problems, from mild aches to true muscle injury. The most serious form, rhabdomyolysis, is rare but dangerous. Seek urgent medical care if you notice:
- Severe muscle pain or weakness that comes on quickly
- Dark, tea-colored or cola-colored urine
- Muscle symptoms together with fever, nausea or feeling very unwell
For milder statin muscle pain, call your prescriber rather than stopping the medicine yourself. They may check a blood test called creatine kinase (CK), look for other causes such as low thyroid function or vitamin D levels, and then decide whether to pause, lower the dose or switch statins. Not every ache in someone taking a statin is caused by the statin.
Keep a simple symptom diary if you notice aches after starting a statin. Note where the pain is, when it began, how strong it is and whether anything else changed, such as a new workout or medicine. This helps your prescriber tell statin muscle pain apart from other causes.
Other risk factors for statin myopathy
SLCO1B1 decreased function is one risk factor among several. Your prescriber looks at the whole picture, which often includes:
- Older age and smaller body size
- Kidney or liver disease
- Untreated low thyroid function (hypothyroidism)
- Higher statin doses
- Interacting medicines, such as gemfibrozil, certain antibiotics like clarithromycin, some antifungals and some HIV medicines
- Large amounts of grapefruit juice with simvastatin, lovastatin or atorvastatin
- Very strenuous exercise, especially when starting a new routine
Many of these can be adjusted. A different antibiotic, a thyroid check or a lower statin dose can bring the overall risk down. Knowing your SLCO1B1 result helps your prescriber decide how much weight to give the other factors when choosing your statin.
Always share a full list of your prescriptions, over-the-counter products and supplements with your pharmacist, particularly when a new antibiotic or antifungal is started.
Who should consider SLCO1B1 testing
SLCO1B1 testing is most useful before or soon after a statin is started, since that is when statin and dose choices are being made. It can also help explain past problems. People who often find it helpful include:
- Anyone about to start a statin, especially simvastatin
- People who stopped a statin because of statin muscle pain
- People who need a high statin dose to reach their cholesterol goal
- People with other risk factors for statin myopathy, such as kidney disease or several interacting medicines
- Relatives of someone known to have SLCO1B1 poor function
The test also covers other drugs. SLCO1B1 affects how some non-statin medicines, such as repaglinide, reach the liver, and its role in other drugs is still being studied. Because the result never changes, testing once can inform future prescriptions for years, even for drugs you do not take today. The PharmGKB database tracks this research if you want to read more.
Testing at home and sharing your result
The RPh Labs at-home PGx kit uses a simple cheek swab. It tests SLCO1B1 as part of a 20-gene panel reported against 240+ medications, and results come 7 to 10 business days after your sample reaches our CLIA-certified lab in Dallas. A PharmD pharmacist reviews each report, and a free pharmacist consultation is included.
The self-pay price is $299, which is HSA and FSA eligible. Insurance, including Medicare, is also accepted; see our insurance page for details.
When your report arrives:
- Look for your SLCO1B1 phenotype and any statins flagged for it.
- Check the ABCG2 and CYP2C9 results too if you take rosuvastatin or fluvastatin.
- Share the full report with your prescriber and pharmacist.
- Ask them to record the result in your chart for future prescriptions.
Never stop a statin or change its dose on your own because of a gene result. Your prescriber weighs it with your cholesterol, heart risk, kidney and liver function and other medicines.
Questions to ask your prescriber about statins and your result
A short, focused conversation gets the most out of your result. Bring the full report, your current medicine list and any notes about side effects you have had with statins in the past, including when they started and how long they lasted.
- Which statin and dose would you choose for me, given my SLCO1B1 result?
- Do my ABCG2 or CYP2C9 results change that choice?
- Are any of my other medicines raising my risk of statin myopathy?
- If I get muscle symptoms, what should I do first, and when should I call you?
- Would a blood test such as CK help if I have symptoms?
- If a statin is not a good fit, what other cholesterol-lowering options exist for me?
It also helps to agree on a plan before symptoms appear. For example, your prescriber may ask you to call rather than stop the statin, so they can check for other causes and adjust the plan quickly. Having that plan in place makes it less likely that a treatable side effect turns into stopping a medicine that protects your heart.
If you see several clinicians, such as a cardiologist and a primary care doctor, make sure each has a copy of your report. Pharmacists can also add your SLCO1B1 result to your pharmacy profile, which helps flag high-risk statin doses when a new prescription is filled. You can find more answers about the test on our FAQ page.
Conclusion
SLCO1B1 is a gene that encodes a transporter primarily responsible for moving a group of compounds that include fatty acids, bile acids, and anionic drugs. It also carries endogenous compounds to the liver, where they are metabolized and either utilized in bodily processes or removed from the bloodstream through excretion. SLCO1B1 decreased function has significant consequences for drug metabolism and patient safety across various therapeutic areas.
At-home Pharmacogenomic testing by RPh LABS provides a clear picture of your SLCO1B1 status and the other genes on its 20-gene panel, facilitating personalized medicine approaches with enhanced efficacy and reduced adverse effects.
References
SLCO1B1 decreased function FAQ
Can I still take a statin with SLCO1B1 decreased function?
Usually, yes. Most people with this result can take a statin. Guidelines suggest choosing the statin and dose with the result in mind, for example avoiding high-dose simvastatin. Your prescriber decides which statin fits your cholesterol goals, heart risk and other medicines.
What is the link between simvastatin and SLCO1B1?
SLCO1B1 helps move simvastatin into the liver. Reduced-function variants leave more simvastatin in the blood, which raises the chance of muscle side effects, especially at higher doses. CPIC suggests an alternative statin or keeping simvastatin below 20 mg a day for people with decreased function.
Does SLCO1B1 poor function mean I will get muscle pain?
No. It means your risk of statin muscle problems is higher than average with some statins, not that you will definitely have them. Many other factors, such as dose, age, kidney function and interacting drugs, also play a part. Your prescriber can choose a statin and dose that lower the risk.
When should statin muscle pain be treated as an emergency?
Get urgent care for severe muscle pain or weakness that comes on quickly, dark or cola-colored urine, or muscle symptoms with fever or feeling very unwell. These can be signs of rhabdomyolysis. For milder aches, contact your prescriber before changing or stopping your statin.
Is the c.521T>C variant the same as rs4149056?
Yes. c.521T>C and rs4149056 are two names for the same SLCO1B1 change. It is found in several reduced-function star alleles, including *5 and *15, and it is the main variant behind most SLCO1B1 decreased function results.
Do I need to repeat SLCO1B1 testing?
No. Your SLCO1B1 genotype does not change during your life, so one test is enough. Guideline advice can be updated as research grows, so keep your report and share it with each new prescriber. RPh Labs updates reports when guidelines change.
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