A senior executive at Europe's largest drug maker has admitted most prescription medicines don't work for most people, it is reported.
Drugs may be more specifically targeted
Allen Roses, of GlaxoSmithKline, is quoted in a national newspaper as saying more than 90% of drugs only work in 30-50% of people.
He said: "Drugs on the market work, but they don't work in everybody."
Mr Roses, an expert in genetics, said new developments should help tailor drugs more specifically.
At present, pharmaceutical companies adopt a "one-drug-fits-all" policy.
But Mr Roses said refinements in genetic technology should make it possible to identify more precisely those people who were likely to benefit from a drug.
He said: "By eliminating the people that we predict will be non-responders we'll be able to do smaller, faster and cheaper drug trials.
"If you can determine who is going to have a response (to a drug) and who is not going to have a response, you can take your next molecule and aim it specifically at the people who haven't had a response with the first one so that you can create a set of drugs that cover the population, and then you are back to selling to everybody."
GSK announced last week that it had more than 20 potential $1 billion-a-year blockbuster drugs in development.
Mr Roses quoted research published three years ago by Brian Spear, an expert in medical diagnostics, which found that different drugs had vastly different success rates in treating patients.
Most drugs had an efficacy rate of 50% or lower.
Richard Ley, a spokesman for the Association of the British Pharmaceutical Industry, told BBC News Online, said Mr Roses' comments emphasised just how important it was to conduct research into new products.
He said: "It's not news to anyone that not all drugs work in all people all the time.
"Sometimes the government and the National Institute for Clinical Excellence want to try to find one drug for a particular condition.
"This shows quite clearly that is not a viable approach. A medicine might work well in one person, and not at all for another."
Cliff Prior, chief executive of mental health charity Rethink, said: "People with mental illness have been telling us for years that different medicines work for different people.
"The idea of pharmacogenetics, that you might have a clue as to which would work best before prescribing it, is excellent.
"But it's still years away from reality. Meanwhile doctors must listen to people taking medicine, and be ready to try a different one if it's not working or if the side effects are bad."