Researchers may have figured out why people respond differently to the same drug.  

Scientists at the University of British Columbia in Canada have untangled genetic and environmental factors related to drug reactions, a step closer to predicting how a drug will affect a person, according to a press release.

"This is a starting reference map for understanding variation in drug response," Guri Giaever, senior author of the study and an associate professor in the University of British Columbia's Faculty of Pharmaceutical Sciences, said in a statement. "It won't be easy but our results suggest it is a solvable problem."

For the study, researchers exposed 6,000 strains of yeast to 3,000 drugs. Yeast strains were modified so their response could be measured. Researchers found that the yeast cells have about 50 main ways in which they react to any drug.

Researchers said the 50 major response types, known as gene signatures, are "like fingerprints that identify all genes and their relevance to a specific drug treatment."

Given this relatively small number of gene mutations, researchers figured that it might be possible to eventually use a person's genome to predict their drug response. This technique could also make it easier to identify more effective therapies.

In a news release, researcher Corey Mislow said the research will help people better understand how and why some drugs work and others don't.

Researchers said their findings may also be relevant cancer treatment.

In the study, Researchers identified all genes that are essential for growth when cells are chemically stressed. Because cancer is principally a cell that grows out of control, the research points to different strategies to develop new drugs that target these genes.

The findings were recently published in the journal Science.