system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do antidepressants cause such different reactions in different people?
gpt
Partially because the medical causes of depression are not well known - brain scans and blood tests of depressed people often show very different information. So prescribing anti-depressants is a guessing game, trying to find one that works for a particular patient is usually a trial and error process. Most antidepressants alter the brain chemistry and affect people in different ways.