The human genome sequence could help scientists find out why a drug that cures one person can kill another.
Scientists say our genetic make-up can often play a big part in the way we react to certain drug compounds.
Researchers hope that data from the human genome project can be used to tailor treatments for more personal care. It could prevent those situations where, for example, an antibiotic may cure a bladder infection in one patient but bring another patient out in a rash.
Dr Wendell Weber, a medical geneticist at the University of Michigan Medical School, US, said that most doctors did not understand the effects of drugs on individuals.
"Physicians and patients understand that genes influence health and disease, but most don't realise the harmful effects pharmaceutical drugs can have on genetically susceptible people," he said.
Dr Weber told the annual meeting of the American Association for the Advancement of Science, in San Francisco, that the completion of the human genome project would have a huge impact on the pharmaceutical industry.
He said it was already known that polymorphisms - variations within a gene - could cause certain racial groups to be more sensitive than others to particular drugs.
"Population frequencies of many polymorphic genes vary with race or ethnic background. For example, a condition called primaquine sensitivity is responsible for the reaction of many African, Mediterranean and Asian men to certain drugs.
"Another mutated gene accounts for the remarkable sensitivity of the Japanese to alcohol," he added.
Dr Weber said he hoped new scientific advances would make drug sensitivity a thing of the past.
"There are millions of polymorphisms in the human genome. Fortunately, only a limited number affect how people react to drugs or environmental substances.
"We already have identified many of them, and data from the human genome project should make it easy to find the others."
Dr Lesley Walker, of the Cancer Research Campaign, said work like this would have a huge impact on the care of diseases like cancer.
"It is hugely important and is the thing that we believe will lead to a large development of treatments and many more tailored to individuals," she said.
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