Subjects in FDA Trials Are Not Representative of the Actual People Receiving Treatment
External validity is the extent to which the results can be generalized to a population of interest. The population of interest is usually defined as the people the intervention is intended to help.
Phase III clinical trials are designed to exclude a vast majority of the population of interest. In other words, the subjects of the drug trials are not representative of the prescribed recipients, once said drugs are approved. One investigation found that only 14.5% of patients with major depressive disorder fulfilled eligibility requirements for enrollment in an antidepressant efficacy trial.
As a result, the results of these trials are not necessarily generalizable to patients matching any of these criteria:
- Suffer from multiple mental health conditions (e.g. post-traumatic stress disorder, generalized anxiety disorder, bipolar disorder, etc.)
- Engage in drug or alcohol abuse
- Suffer from mild depression (Hamilton Rating Scale for Depression (HAM-D) score below the specified minimum)
- Use other psychotropic medications
These facts call into question the external validity of standard efficacy trials.
Impossible to Discover Effectiveness for All Conditions
The fact that co-morbidities are excluded also makes it impossible to discover potential new uses for a treatment.