Final answer:
When unexpected side effects are discovered in a drug during post-market surveillance, both the regulatory agency and the company will take action to ensure safety. The regulatory agency may require additional studies and the company will work with them to investigate, update labeling, and implement safety measures.
Step-by-step explanation:
When a post-market surveillance of a drug reveals unexpected side effects in some people, both the regulatory agency and the company will likely take action. The regulatory agency, such as the FDA in the United States, will review the safety data and may require additional studies or impose restrictions on the drug. The company will work with the regulatory agency to investigate the side effects, update the drug's labeling, and possibly implement additional safety measures.