How do you determine whether different medicines will cause side effects in different people with different conditions,

Question: How do you determine whether different medicines will cause side effects in different people with different conditions, for example people with certain allergies? Does it involve clinical trials or do you take a different approach?
- Keywords:
  medicine,
  side effect
Asked by yorkylass to Thorrun on 18 Jun 2017.
- Thorrun Govind answered on 18 Jun 2017:
  
  Sometimes it a case of trial and error and it can be spotting the side effects by talking to patients and stopping medications before these side effects cause big problems. In a community pharmacy we can’t check blood levels and eg liver function but we can spot early issues and refer to doctor.

Question: How do you determine whether different medicines will cause side effects in different people with different conditions, for example people with certain allergies? Does it involve clinical trials or do you take a different approach?