Millions of people are prescribed medications based on efficacy trials with as few as 20 participants.
Due to exclusion criteria and added cost, patient sample sizes are very small. The number of subjects per trial on average is:
- 275 patients are sought per cardiovascular trial
- 20 patients per cancer trial
- 70 patients per depression trial
- 100 per diabetes trial
You can look up the efficacy and trial size for any drug at https://dailymed.nlm.nih.gov. On a drug page, scroll down to the “CLINICAL STUDIES” section to see the efficacy tables. Here’s the data for Immediate-Release Bupropion (Wellbutrin).