Davis, Alison. (2006). Medicines By Design. Bethesda, MD: National Institute of General Medical Sciences, National Institutes of Health, U.S. Department of Health and Human Services. 54 p. NIH Publication No. 06-474. html pdf
"Your genes can also affect how you respond to the medicines you take. ... One important group of proteins whose genetic code varies widely among people are “sulfation” enzymes, which perform chemical reactions in your body to make molecules more water-soluble, so they can be quickly excreted in the urine. Sulfation enzymes metabolize many drugs, but they also work on natural body molecules, such as estrogen. Differences in the genetic code for sulfation enzymes can significantly alter blood levels of the many different kinds of substances metabolized by these enzymes. ... Lab tests revealed that sulfation enzymes manufactured from genes with different spellings metabolize drugs and estrogens at different rates (p. 8)."