Plan B

Raw research findings for this medication. Mostly single studies, not curated or confirmed robust.

About Plan B

What it is

Levonorgestrel is a progestin used for contraception: as an emergency contraceptive pill taken soon after unprotected sex (Plan B), in hormonal coils (Mirena, Kyleena, Skyla) that also treat heavy periods, in implants (Jadelle) and in many combined pills.

How genes come into it

Levonorgestrel is broken down mainly by CYP3A4. Most gene studies on it looked at women using the implant while taking efavirenz for HIV: efavirenz speeds up CYP3A4, and women with slow CYP2B6 versions, who have higher efavirenz levels, had the lowest levonorgestrel levels. Studies also looked at NAT2 and UGT1A1. There is no CPIC or DPWG guideline.

What research found

Every published finding on gene variants and Plan B. Upload your DNA file to see which of these rows apply to you.

Metabolism (7 findings)

Studies of how quickly the body processes this medication.

CYP2B6 CYP2B6 poor metabolizer: CYP2B6 poor metabolizer is associated with increased clearance of levonorgestrel in women with HIV Infections as compared to CYP2B6 normal metabolizer.

CYP2B6 rs3745274: Genotypes GT + TT are associated with decreased concentrations of levonorgestrel in women with HIV Infections as compared to genotype GG.

CYP2B6 rs4803419: Genotype CT is associated with decreased concentrations of levonorgestrel in women with HIV Infections as compared to genotype CC.

CYP2B6 CYP2B6 intermediate metabolizer: CYP2B6 intermediate metabolizer is not associated with increased clearance of levonorgestrel in women with HIV Infections as compared to CYP2B6 normal metabolizer.

Study findings and evidence levels: PharmGKB (CC BY-SA 4.0). Guidelines: CPIC and DPWG, as bundled in PharmCAT. Most studies were done mainly in people of European ancestry.

Related Drugs

More drugs from the same category

Provera (Progestins)

Actos (Thiazolidinediones)

Amaryl (Sulfonylureas)

Not a prescribing recommendation. This page is educational information about pharmacogenomic research and clinical guidelines - it is not medical or dosing advice, and not a prediction of how any medication will work for you. Never start, stop, or change a medication or dose based on it; talk to your doctor or pharmacist, who can order clinical-grade testing if appropriate.

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Content updated September 2026.

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