The development of this Clinical Guideline document was led by national working groups comprised of clinical and academic experts from the fields of seniors' mental health, geriatrics, and substance use and addictions. Each working group included a person whose life has been directly impacted by a substance use disorder. The Guidelines all reflect the fact that older adults are much more vulnerable to the potential adverse effects of these substances and that most individuals are also taking a variety of prescribed medications and over-the-counter products which can result in dangerous interactions.