Why do antidepressants and antipsychotics affect different people differently?

Meds: The two different meds are formulated to affect different areas of the nervous system/brain by the manufacturer. That being said, medication prescription is an art much more than it is a science. It all depends on the patient and prescriber, and whether or not the med is being taken responsibly. It's painstaking trial-and-error much of the time. And the body's needs can change over time.

Good question: There are many reasons. Different people have different genetic make-up which includes differences in the way we metabolize medications .People also have different body mass which means different dosages maybe required. We have different renal & liver function which have to do how we change and get rid of medications in our body. Also there can be many psychological variables which impact symptoms