From UPI.com:

U.S. scientists say they're using DNA extracted from saliva to customize prescriptions and solve dosing problems that often confound doctors and patients.

By using DNA to customize a prescription, researchers at Temple University's School of Pharmacy hope to prevent adverse drug reactions. At the top of the list of problem drugs is warfarin (Coumadin), the most widely prescribed anticoagulant.

The researchers say they're trying to find the correlation between genotypes and the correct dosage of warfarin. By collecting saliva samples and extracting DNA, the scientists can look for variances in genetic clues that make people metabolize the same drug in very different ways.

"Our findings have confirmed there is a genetic variance of certain genotypes that correlate to how these participants respond to this drug," said Associate Professor Nima Patel, one of the investigators. "So, if you have this genotype, we can conclude what your risks may be, based on your DNA."

That would allow doctors to prescribe the correct dosage of warfarin and decrease the risk of adverse drug reactions.