Isn't the effectiveness of ssri/snri's on person with depression directly dependent on the person's natural production of serotonin and/or norepinephrine? and therefore they would be useless in someone who produces little to none?

Yes it is true: .. That these medications need native serotonin and norepinephrine to work. And everyone makes these neurotransmitters. So that is why we need to use the medications carefully.

Think postively: It sounds as if you might be trying to think of a reason why you shouldn't take antidepressants. There are various approaches to deal with depression and antidepressant medication is one of them. There are several different types Sometimes therapy is the treatment of choice and frequently a combination of both of them. There is lots of research demonstrating the effectiveneness of such medications

SSRI/SNRI meds: SSRI/SNRI meds are remarkably effective for depression and anxiety disorders because they boost the efficacy of serotonin and norepinephrine already in the brain. They don't increase the absolute levels of these brain hormones. These meds must be carefully monitored by your doctor for a therapeutic response and side effects. Hope this helps.