system
Given the following post, respond as if you're commenting on Reddit:
human
Why can a single individual react so differently to drugs in the same family (i.e. Xanax vs Ativan, both benzodiazepines)? And why do different individuals experience just as much variance between drugs, but not the same experiences on the same drugs as other individuals?

I hope I was coherent, but I'll give some examples to clarify. 

Individuals A and B have been prescribed both Xanax and Ativan. (A) reports that Xanax has had a stronger effect on their anxiety, while Ativan is too mild and ineffective. (B) reports that Ativan is stronger and more effective, while his Xanax is too mild. 

Assuming similar BMI, same sex, and same treatment method, why are the experiences so different?
gpt
* Because there is a tremendous amount of molecular variation from person to person, due to both genetics and environmental factors (including exposure to other drugs and other non-drug chemicals).
 * Because drugs are put in the same class based on the therapeutic effect they have, but they still have a tremendous amount of variation in chemistry, which includes how quickly they are absorbed, how much they are absorbed, how quickly they are excreted, etc. Even small chemical differences between drugs can lead to dramatically different potency and effects.