Mayo Clinic researchers gave a presentation 12/11/08 at the 31st annual San Antonio Breast Cancer Symposium that further confirms the importance of the liver enzyme CYP2D6 in individualizing tamoxifen dosing in breast cancer patients. Tamoxifen is often prescribed to block the effects of estrogen in breast tissue preventing breast cancer recurrence in ER+ (estrogen receptor positive) cancers which require estrogen to grow and spread.

Psychological disorders are complex and the number of treatments available in the United States continues to grow but virtually all medications used to treat depression are metabolized by two enzymes in the liver: CYP2D6 and CYP2C19. Your genes are the main factor determining the level of these enzymes-if you have too much of the enzyme you process the medication too quickly too little of the enzyme and the medication builds up in your bloodstream potentially causing adverse reactions or side effects.