The prevalence of opioid therapy for chronic noncancer pain has increased dramatically in recent years, with a parallel increase in opioid abuse, misuse and deaths from accidental overdose. We review epidemiological and clinical data that point to the important roles psychiatric disorders have in the use and abuse of opioids in patients with chronic pain.

We conducted literature searches on the PubMed with the key phrases “chronic pain” and “opioid therapy” and selected those articles on the epidemiology of comorbidity between chronic pain and psychiatric disorders, the trends in long-term opioid therapy and the clinical trials that involved using opioid therapy for chronic pain or for mental health disorders. We then thoroughly reviewed the bibliography of all relevant articles to identify additional papers to be included in the present review.

Chronic pain is highly comorbid with common psychiatric disorders. Patients with mental health and substance abuse disorders are more likely to receive long-term opioid therapy for chronic pain and more likely to have adverse outcomes from this therapy. Although opioids may exert brief antidepressant and anxiolytic effects in some patients with depression or anxiety, there is scant evidence for long-term benefit from opioid treatment of psychiatric disorders.

Opioids may be used in current clinical practice as the de facto and only psychiatric treatment for patients with chronic pain, despite little evidence for sustained benefit. The opioid epidemic thus reflects a serious unmet need for better recognition and treatment of common mental health problems in patients with chronic pain. Psychiatry is the missing P in chronic pain care.