Data on the most obvious side effects are collected in the first phase which is a very small group of healthy patients who take the drug under medical supervisi

Data on the most obvious side effects are collected in the first phase which is a very small group of healthy patients who take the drug under medical supervision in increasing doses until the side effects are so bad they can't keep going. They use this data to establish safety limits for the rest of the clinical trial and continue monitoring the situation until well after the drug is approved.