• T (minor) allele results in non-functional CYP2D6*4 protein.
  • C (major) allele results in normal levels of CYP2D6*4 protein

The Minor "T" allele is associated with:

  • 3-8X Parkinson's risk upon exposure to pesticides based on dose (R,R2).
  • Lower benefits of the drug Tomoxifen, whose active form is formed via CYP2D6 metabolism.
  • More side effects to TCA drugs because of slow metabolizing.
  • ~4x increased risk Bradycardia from beta blockers (R).
  • 6 fold more side effects upon switching antidepressants (TT) (R).
  • Lower maintenance doses of antidepressants (TT) (R).
  • Lower risk of bladder and lung cancer (R).
  • Less severe neurodegeneration in Alzheimer's (R).
  • Poor metabolism of debrisoquine (TT) (R).

Some drugs are typically first metabolized by CYP2D6 include:

  • dextromorphan
  • sparteine
  • metoprolol
  • nortriptyline
  • many antidepressants
  • codeine


Parent Gene: CYP2D6

Importance: 3
Less common allele: T = 9%
More common allele: C = 91%
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