As others have mentioned, if adverse side effects are observed after the product was used/administered by a patient during a clinical trial, it is most likely paused until effects go away and a solution is found as to what is causing the effects. For most drugs, there would be side effects such as rashes, allergies, etc. however more severe side effects can pause a trial. In extreme cases, if death occurs to a patient that will most likely stop the clinical trial in its tracks. An investigation would occur that can take up to over a year and the drug/product would have to be updated to make sure this does not occur again.