Sometimes, putative medical adverse effects are regarded as controversial and generate heated discussions in society and lawsuits against drug manufacturers. One example is the recent controversy as to whether autism was linked to the MMR vaccine (or by thiomersal, a mercury-based preservative used in some vaccines). No link has been found in several large studies, and despite removal of thimerosal from vaccines a decade ago the rate of autism has not decreased as would be expected if it had been the causative agent.