In the '90s a fifth of all new drugs licensed in the US were later found to have serious or life-threatening side effects. These had been unknown to or undisclosed by the manufacturer when the drug was approved. The implications are frightening. In the case of five drugs withdrawn during the twelve months September '97 - '98, 20 million patients (10% of the US population) had already been exposed to possible danger. The study also reported that new drugs' side effects could take up to seven years to show up.

Adopting the precautionary principle, health research group Public Citizen advised people to wait five years before taking any new drug.