Our neurochemistry is all unique. Even within the same disorder, much less in dealing with something like PTSD which -to the best of my knowledge- can hit anyone. Neurotypical or Comorbid. (Anxiety, Autism, ADHD, Bipolar Disorder, <insert rest of DSM here ;)>, most of which have their own unique quirks to how the brain reacts to chemicals that are different from neurotyoical people and different for people who have different disorders.)
Add in that what a drug is "labeled" for (a highly political & extremely expensive process; hundreds of millions of dollars) is very often not what it's best use is for? It's not as simple as depressed = antidepressant.
So when starting any course of medication? Know that it's a very collaborative process... Since we don't have a way to scan your unique brain & determine what will work, work best, or work badly for you... The only way to find out is to try.