Simvastatin (Zocor) and SLCO1B1 Pharmacogenomics

Q: Why is simvastatin affected by genetics?

Simvastatin relies on the SLCO1B1-encoded OATP1B1 transporter to enter liver cells, where it lowers cholesterol. Genetic variants that reduce OATP1B1 function lead to higher simvastatin levels in the bloodstream, increasing the risk of muscle-related side effects (myopathy).

Q: What is statin-associated myopathy?

Statin-associated myopathy refers to muscle symptoms — pain, tenderness, or weakness — that occur during statin therapy, sometimes accompanied by elevated creatine kinase levels. In rare cases, severe myopathy can progress to rhabdomyolysis, a potentially life-threatening condition involving muscle breakdown.

Q: Which gene affects simvastatin response?

SLCO1B1 is the primary gene with CPIC Level A evidence for simvastatin. It encodes the OATP1B1 hepatic transporter. The key variant is rs4149056 — the C allele reduces transporter function and increases myopathy risk.

Q: What do CPIC guidelines recommend for simvastatin?

For patients with intermediate SLCO1B1 function (TC genotype at rs4149056), CPIC recommends a lower simvastatin dose or an alternative statin. For poor function (CC genotype), CPIC recommends avoiding simvastatin or using a low dose with careful monitoring. Alternative statins like pravastatin or rosuvastatin have lower myopathy risk.

Q: Is simvastatin the only statin affected by SLCO1B1?

Simvastatin has the strongest evidence for SLCO1B1-related myopathy risk and is the focus of the CPIC guideline. Other statins are also transported by OATP1B1, but the clinical impact varies. Pravastatin, rosuvastatin, and fluvastatin generally carry lower myopathy risk and are commonly recommended as alternatives.

Q: Can consumer DNA data assess simvastatin myopathy risk?

Yes. The key SLCO1B1 variant rs4149056 is well-covered on consumer genotyping arrays from 23andMe, AncestryDNA, and other services. Consumer-grade analysis can reliably determine your SLCO1B1 genotype and flag the simvastatin interaction if relevant.

Last updated: February 2026

What Is Simvastatin?

Simvastatin (brand name Zocor) is a widely prescribed statin medication used to lower LDL cholesterol and reduce cardiovascular risk. Statins work by inhibiting HMG-CoA reductase, the rate-limiting enzyme in cholesterol synthesis. Simvastatin has been one of the most commonly prescribed statins worldwide, with proven benefits in reducing heart attacks, strokes, and cardiovascular mortality.

What makes simvastatin relevant to pharmacogenomics is that its safety profile is influenced by a genetic variant in SLCO1B1, the gene encoding a liver transporter that controls how efficiently simvastatin enters hepatocytes. Patients with reduced SLCO1B1 function face a higher risk of statin-associated muscle side effects — a concern that can be anticipated through genotype testing.

Why Simvastatin Response Varies by Genetics

Simvastatin is administered as an inactive lactone prodrug and converted to its active acid form in the body. The active acid must be transported into liver cells by the OATP1B1 transporter (encoded by SLCO1B1) to reach its target enzyme and exert its cholesterol-lowering effect.

When OATP1B1 function is reduced due to genetic variants, simvastatin acid is not efficiently cleared from the bloodstream. Higher circulating levels mean greater exposure of muscle tissue to the drug, which increases the risk of myopathy. Understanding this transport mechanism is key to how pharmacogenomic testing can inform statin prescribing.

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SLCO1B1 and Statin-Related Muscle Effects

Statin-associated myopathy encompasses a spectrum of muscle symptoms, from mild muscle aches to the rare but serious condition of rhabdomyolysis. The risk is dose-dependent — higher statin doses carry greater risk — and is modulated by SLCO1B1 genotype:

Normal Function (TT at rs4149056): Standard OATP1B1 transporter activity. Simvastatin is cleared into liver cells efficiently. Standard myopathy risk at recommended doses.
Intermediate Function (TC): One reduced-function allele. Moderately elevated simvastatin acid levels in circulation. The SEARCH trial found a 4.5-fold increased myopathy risk with the 80 mg dose in TC carriers.
Poor Function (CC): Two reduced-function alleles. Substantially elevated simvastatin levels. Highest myopathy risk. CPIC recommends avoiding simvastatin or using a low dose.

It is important to note that not everyone with reduced SLCO1B1 function will experience muscle symptoms. Genetics is one risk factor among several, including dose, age, kidney function, drug interactions, and physical activity level. The goal of genotype-guided prescribing is to reduce risk, not to predict symptoms with certainty. For a plain-language explanation of how reduced-function genotypes affect drug processing, see what does poor metabolizer mean.

CPIC Guideline Summary

The SLCO1B1–simvastatin interaction has a CPIC Level A classification — the strongest evidence level. The guideline recommends:

Normal Function (TT): Standard simvastatin prescribing. No genotype-based adjustments needed.
Intermediate Function (TC): Prescribe a lower simvastatin dose or consider an alternative statin with lower myopathy risk (e.g., pravastatin, rosuvastatin, fluvastatin).
Poor Function (CC): Avoid simvastatin or use a low dose with careful monitoring. An alternative statin is generally preferred.

Note that the 80 mg simvastatin dose was restricted by the FDA in 2011 for new patients regardless of genotype, due to elevated myopathy risk at that dose level.

Already have your DNA file? See if simvastatin is flagged for your SLCO1B1 genotype.

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Clinical Context and Evidence

The SEARCH trial (Study of the Effectiveness of Additional Reductions in Cholesterol and Homocysteine; Link et al., 2008; PMID: 18855540) was the pivotal study that identified the SLCO1B1 rs4149056 variant as a major genetic risk factor for simvastatin-induced myopathy. The trial found that the C allele at rs4149056 was present in 60% of myopathy cases on the 80 mg simvastatin dose, compared to 19% of controls.

Subsequent studies have confirmed this association across different statin doses and populations. The relationship between SLCO1B1 genotype and simvastatin myopathy is one of the most well-replicated pharmacogenomic findings in clinical medicine, supporting the CPIC Level A classification.

Understanding Your Results

If you have raw DNA data from 23andMe, AncestryDNA, or another consumer service, DecodeMyBio can determine your SLCO1B1 genotype and report whether simvastatin is flagged as a drug-gene interaction. Your Medication Safety Report will include your SLCO1B1 genotype, function category, and the CPIC recommendation for simvastatin. You can view a sample report to see the format.

Statin prescribing involves balancing cardiovascular benefit against side effect risk. If your report identifies reduced SLCO1B1 function, this does not mean you should avoid all statins — alternative statins with lower myopathy risk may be appropriate. Always discuss results with your healthcare provider. See our methodology and limitations pages for important context about consumer-grade analysis. To see how DecodeMyBio compares to other pharmacogenomic testing options, visit our testing comparison page.

Get your Medication Safety Report. Upload your raw DNA data to see your SLCO1B1 results and statin safety profile.

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Related Resources

Frequently Asked Questions

Why is simvastatin affected by genetics?

Simvastatin relies on the OATP1B1 transporter (encoded by SLCO1B1) to enter liver cells. Genetic variants that reduce transporter function lead to higher drug levels in the bloodstream and increased muscle side effect risk.

What is statin-associated myopathy?

Myopathy refers to muscle symptoms — pain, tenderness, or weakness — during statin therapy. In rare cases it can progress to rhabdomyolysis. The risk is dose-dependent and modulated by SLCO1B1 genotype.

Which gene affects simvastatin response?

SLCO1B1 is the primary gene with CPIC Level A evidence. The key variant is rs4149056 — the C allele reduces hepatic transporter function and increases myopathy risk.

What do CPIC guidelines recommend for simvastatin?

For intermediate function (TC genotype), CPIC recommends a lower dose or an alternative statin. For poor function (CC), CPIC recommends avoiding simvastatin or using a low dose with monitoring.

Is simvastatin the only statin affected by SLCO1B1?

Simvastatin has the strongest evidence. Other statins are also transported by OATP1B1, but pravastatin, rosuvastatin, and fluvastatin generally carry lower myopathy risk and are common alternatives.

Can consumer DNA data assess simvastatin myopathy risk?

Yes. The key variant rs4149056 is well-covered on consumer arrays from 23andMe, AncestryDNA, and other services. Consumer analysis can reliably determine your SLCO1B1 genotype and flag the simvastatin interaction.

Last reviewed: February 2026 · DecodeMyBio Editorial Team