The safety concerns are so serious that the drug either is pulled from the market, or the drug regulator is forced to issue special warnings that the drug can have fatal effects.
The dangers of the new drugs often don't come to light until four years after they have been licensed, which means that many thousands of patients may have been affected. But in every case, doctors and patients believed the drugs were safe because they had passed all the usual tests for safety and effectiveness.
Researchers from the Brigham and Women's Hospital in Boston uncovered the failures in safety testing when they looked at the track record of 222 new drugs that had been passed as safe by America's drug regulator, the Food and Drug Administration (FDA), between 2001 and 2010. One in three of these had a 'safety event', the researchers discovered, which included three drugs which were withdrawn because they were so dangerous, 61 had 'boxed warnings'—the FDA's most serious alert before a drug is taken off the market, and means the drug may be a killer—and 59 had their safety questioned.
"These safety risks emerge, on average, four years after approval. This means that many patients are exposed to these medications before the risks become clear," said lead researcher Nicholas Downing.