A 39-year-old veteran presents with comorbid posttraumatic stress disorder (PTSD) and substance abuse. Her care provider recommends addressing her PTSD and substance use disorder (SUD) simultaneously. Which of the following statements is true regarding managing co-occurring PTSD and SUD?

a) Treat PTSD first before addressing SUD
b) Address SUD first before treating PTSD
c) Simultaneously address both PTSD and SUD
d) PTSD and SUD are unrelated conditions