That problem is likely to grow. "There are still a relatively small number of drugs where pharmacogenomics actually plays a role, but this could drastically expand over the next five years," says Scott Weiss, a physician at Harvard Medical School and interim director of the Partner's Healthcare Center for Personalized Genetic Medicine. "Antidepressants, asthma meds, anti-arrhythmia drugs, lipid-lowering drugs--some of the biggest sellers in terms of drug use nationally could potentially have pharmacogenetic implications."

Medco is also funding studies to evaluate the cost-effectiveness of specific pharmacogenomics tests, including those for the blood thinner warfarin and the breast cancer drug tamoxifen. The company will announce results of a study conducted in collaboration with the Mayo Clinic at the American College of Cardiology conference next month.

By acquiring DNA Direct, Medco greatly expanded its ability to offer genetic tests and the decision-making tools needed to put them into practice. "We were concentrated on a dozen pharmacogenomic tests," says Epstein. DNA Direct, on the other hand, "has expertise in 1,000 to 2,000 tests."

Founded in 2005, DNA Direct began as a direct-to-consumer genetic testing company. The company has gradually expanded its offerings, developing decision-making software to help physicians and patients decide when genetic testing is appropriate and what to do with the results. It has also created a network of genetic counselors to answer questions, as well as partnerships with insurers to determine which tests should be covered for which patients.

Medco plans to launch a new set of tools based on DNA Direct's existing infrastructure and present them to clients this summer. "Patients are going to see the principles of personalized medicine presented to them rather dramatically," says Edward Abrahams, executive director of the Personalized Medicine Coalition, a Washington, DC-based advocacy organization comprised of payors, providers, industry, academia and patient advocacy groups.