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CYP2B6 is a detox enzyme that processes drugs such as efavirenz, bupropion, cyclophosphamide, and thiotepa. The CYP2B6 gene is highly variable, and people with different variants have different enzyme activity. That explains why these drugs have different effects in different people. Read on to find out more about this enzyme, gene variants, and factors that increase or decrease its activity.



CYP2B6 is one of the cytochrome P450 monooxygenases (CYPs). These are enzymes that eliminate most of the drugs and toxins from the human body (R).

Read more about CYPs here.

CYP2B6 Function

This enzyme metabolizes:

CYP2B6 Gene Polymorphism

With over 100 described SNPs, CYP2B6 is one of the most variable CYP genes in humans (R).

rs3745274 (T) is the most common and clinically significant variant. It results in markedly reduced enzyme activity (R).

It is significant because it occurs commonly (particularly in Africans, Asians, and Hispanics) and influences important drugs that are processed by CYP2B6 (e.g. efavirenz, bupropion, cyclophosphamide) (R).

The T variant is associated with slower metabolism of bupropion (it stays active longer) (R). In adult smokers, T was associated with higher abstinence rates (423 subjects) (R).

This variant was more frequent in nicotine dependent individuals (421 subjects) (R).

People with the T variant have a lower clearance of ketamine. This results in higher drug levels that may be associated with more frequent ketamine adverse effects (49 chronic pain patients) (R).

The T variant is associated with a slower metabolism of efavirenz (R). This means people with this variant will have increased efavirenz exposure and nervous system-related adverse effects (821 subjects) (R).

Similarly, this variant increases nevirapine exposure. Children with T/T had improved immunological responses to this drug (126 subjects) (R).

On the other hand, CYP2B6 converts cyclophosphamide to its active form. Patients carrying at least one T are significantly less likely to achieve a complete response after chemotherapy with fludarabine plus cyclophosphamide (455 subjects) (R).

People with G in this position have a higher clearance and a lower level of (S)-methadone (366 subjects) (R).

People with rs28399499 C have lower enzyme activity.

C variant increases efavirenz and nevirapine levels (821 and 371 subjects respectively) (R, R).

People with rs2279345 T have a higher clearance and therefore a lower level of (S)-methadone (366 patients) (R).

G increases enzyme activity (64 subjects) (R).

Smokers with A/A had higher smoking cessation success rate on bupropion therapy (478 subjects) (R).

A/G women with liver-metastatic breast cancer had a 47% reduced risk of death and a 6-month-longer overall survival on docetaxel and thiotepa therapy (153 patients) (R).

Both C/T and T/T prolonged survival in breast cancer patients with liver metastasis on docetaxel and thiotepa therapy (153 patients) (R).

Increasing or Decreasing CYP2B6

These increase CYP2B6:

  • 17β-estradiol (E2) at high concentrations (R).

These decrease CYP2B6:

FDA Compliance

The information on this website has not been evaluated by the Food & Drug Administration or any other medical body. We do not aim to diagnose, treat, cure or prevent any illness or disease. Information is shared for educational purposes only. You must consult your doctor before acting on any content on this website, especially if you are pregnant, nursing, taking medication, or have a medical condition.


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