Estimations of the extent and significance of anxiety and depressive disorders in chronic pain sufferers are not always consistent. Differences in the definition of chronic pain, regarding pain intensity, pain duration, and pain sites as well as differences in sampling methods, including setting and geographical location, can all contribute to variance in prevalence estimates and other measures. Nevertheless, conventionally defined anxiety and depressive disorders appear significantly more frequent among people with chronic pain than those without.

A national survey in the United States showed that among chronic pain sufferers, 35.1% experienced anxiety disorders and 20.2% experienced depressive disorders in the past year, whereas the respective numbers in the general population are 18.1% and 9.3%.² Another national survey³ found similar rates for anxiety, 26.5%, and depression, 17.5%. Again, these estimates are roughly 1.5 to 2 times as high as those in the general community, which are 18.1% and 9.5% for anxiety and depression, respectively, in the United States.⁴

A large household survey in Canada⁵ also showed that the rate of depression present in people with chronic pain, 19.8%, is more than 3 times as great as in those without pain (5.9%).

Demyttenaere et al.⁶ carried out 18 surveys in 17 countries representing all five continents (N = 85,088). It was reported that “mental disorders” are more common in people with chronic pain than those without, with a pooled odds ratio (OR) of 2.7 for anxiety disorder, 2.1 for agoraphobia or panic disorder, 1.9 for social phobia, 2.6 for posttraumatic stress disorder (PTSD), 2.3 for major depression, and 2.8 for dysthymia. With further analyses of the same data, the researchers found that mood and anxiety disorders are more prevalent in people with multiple pain sites than those without one pain site and those without.⁷ Relative to people without pain, the pooled estimates of odd ratios were 1.8 and 1.9 for mood disorder and anxiety, respectively, among people with single pain site and 3.6 and 3.7 among people with multiple pain sites.⁷

Ohayon and Schatzberg⁸ conducted a survey in five European countries, including the United Kingdom, Germany, Italy, Portugal, and Spain. It was found that 43.4% of the subjects with major depressive disorder suffer from chronic pain, which is 4 times more often than in subjects without major depressive disorder.

Another large survey representing 15 European countries suggested that the prevalence of self-report diagnosis of depression associated with chronic pain is 21%.⁹

The results reported earlier are from population-based studies. It is perhaps not surprising that the estimates of the prevalence of anxiety and depression are higher in pain sufferers identified in clinical settings than those in the general population. A survey of patients (N = 5,808) visiting a primary care clinic showed that chronic pain is more commonly reported in people with major depressive disorder, 66%, than those without, 43%. In particular, disabling chronic pain is substantially more common in people with major depressive disorder, 41%, than those without, 10%.¹⁰ In a study of 1,204 consecutive adults attending a specialty pain service in London, 60.8% met screening criteria for probable depression, and 33.8% met criteria for severe depression on a commonly used, validated, screening questionnaire.¹¹ In a literature review of depression and pain comorbidity,¹² the rates for concurrent major depression in pain sufferers were identified as 18% (4.7% to 22%) in population-based settings and an average of 13% to 85% in various clinical settings. Among the 42 studies reviewed, 33 explicitly focused on chronic pain.

The high rates of anxiety and depression in chronic pain are worrying, particularly given that the consequences of these disorders with respect to overall health. In the most updated World Health Organization (WHO)¹³ report of global health, depression is ranked as the single largest contributor to global disability, and anxiety disorders the sixth. Depression was also reported to be the major contributor to suicide deaths, with number close to 800,000 per year. It was estimated that 4.4% of the global population are suffering from depression and 3.6% from anxiety.¹³ However, in contrast to the high prevalence and significant consequent health loss of these mental disorders, results from WHO surveys also showed that the proportion of people with access to treatment for mental disorders are far lower than that for physical disorders in developed countries, even more so in developing countries, and even for those people assessed as having a severely disabling condition.¹⁴

The association between the concurrence of depression and pain and the impairment in functioning has been well documented. In a large-scale survey representing five European countries (N = 21,425), it was reported that people with pain and depression experience decreased work productivity on more than twice as many days per month as those with either condition alone, and more than 5 times as many days per month as those without either condition.⁶ It has also been reported that patients with pain and depression have higher unemployment rates.^11,12,15,16 In a review of 22 studies on comorbidity between depression and pain, it was identified that patients with depression and pain experience impaired social functioning; functional limitations, such as limited mobility and limitation in activities; more days of illness; and more hospitalizations compared to those with pain alone.¹²

In people seeking specialty treatment for chronic pain, those screening positive for probable depression incur 60% higher total health care costs compared to those who do not screen positive.¹¹ In this study, the significantly greater costs remained for those with severe depression even after adjustment for the role of age, gender, occupational status, the presence of generalized pain, pain interference, and pain acceptance.

Although it is based on fewer smaller studies, there is also evidence showing the impact of anxiety disorders in combination with pain. In a recent survey of 80 patients with chronic neck pain, it was observed that anxiety is associated with greater functional disability.¹⁷ In a study of 250 chronic musculoskeletal pain patients in a primary care in the United States,¹⁸ 45% of the patients screened positive for at least one anxiety disorder and, as compared to those without any anxiety disorder, showed significant worse health status on a range of pain, psychological, and other quality of life-related outcomes. These patients with anxiety conditions also showed substantial functional impairment, the extent of which was strongly associated with the extent of anxiety disorders, in that higher numbers of anxiety conditions were associated with more severe pain-related interference, worse mental health, and more days of disability.

An expanding body of literature has also shown associations between chronic pain conditions, comorbidity with mental health problems, and suicide.^{19,20,21,22,23,24} A survey suggested that 50% of chronic pain patients had serious thoughts of committing suicide due to their pain disorder.¹⁹ Specific pain-related risk factors, such as pain severity and comorbidity with depression, have been suggested as accounting for the increased rates of suicidal behavior in chronic pain patients.²⁰ Data from a large-scale survey of Canadian population²³ showed that after controlling for demographics, Axis I mental disorders, and comorbidity (three or more mental disorders), the presence of one or more chronic pain conditions was associated with both suicidal ideation and suicidal attempt. Among those with a mental disorder, comorbidity with one or more chronic pain conditions was also associated with suicidal ideation and suicidal attempt.²³ Braden and Sullivan²¹ investigated the independent association between noncancer chronic pain conditions and the risk for suicidal behavior, using data from a national survey (n = 5,692). The results suggested that after controlling for medical, mental health, and demographic variables, the presence of any pain condition was associated with lifetime suicidal ideation, OR 1.4 (95% confidence interval [CI], 1.1 to 1.8). Data from the same survey similarly identified head pain and a summary pain score as potentially independent risk factors for suicidal ideation and suicide attempt.²²

The comorbidity of chronic pain with depression and anxiety has also shown association with problematic substance use (e.g., Feingold et al.²⁵). In a study including 888 individuals receiving treatment for chronic pain,²⁵ depression was found present in 88% of the participants with problematic use of opioids and 46.5% of those with problematic use of cannabis, and the prevalence of anxiety was 74.5% and 41.9%, respectively. The results also revealed that any diagnosis of depression, particularly moderate to severe and severe depression, and also generalized anxiety disorder (GAD), again more so with greater severity, were significantly associated with problematic use of opioids and cannabis.

A general finding is that chronic pain sufferers with anxiety and/or depression demonstrate significantly worse quality of life compared to those without.²⁶ Together with the aftermath of suicide, or problems in the wake of substance abuse, they reflect what is arguably the worst possible quality of life.

Once again, there is significant variability in the evidence surrounding rates and impacts of anxiety and depressive disorders in chronic pain sufferers. For instance, in patients suffering from pain and co-occurring depression, depression may be misdiagnosed due to shared symptoms between pain and depression (e.g., sleep disturbance and weight and appetite changes). Caution is warranted in any attempts at higher precision interpretations of these findings. Nevertheless, numerous studies generally demonstrate a high rate of concurrence of anxiety and depressive disorders with pain as well as the additional important burden of anxiety and depression disorders on chronic pain suffers, as observed in a wide range of outcomes.

There has been a long running debate about the relationship between chronic pain and psychopathology associated with anxiety and depression in terms of which comes first or whether one ought to be appropriately regarded as the cause of the other. Available evidence allows for contrasting interpretations. For instance, patients with preexisting depression were found to be more likely to develop chest pain and headache.²⁷ On the other hand, in a related review of available evidence at the time, it was suggested that depression is most often a consequence and follows the development of pain.²⁸ More than 20 years ago, a model called the “diathesis-stress model” was proposed,^29,30 consistent with this view. In this model, the diatheses are conceptualized as preexisting semidormant characteristics of the individuals before the onset of chronic pain that are then activated by the stress of chronic pain condition. Bank and Kerns²⁹ identified the experience of chronic pain itself as the stress component of the model. The researchers also suggested that chronic pain is more likely to result in depression than other chronic medical conditions due to the uniquely challenging nature of stressor associated with chronic pain.²⁹ Dohrenwend et al.³¹ investigated this hypothesis with a family study for people with myofascial face pain, using psychiatric interviews. The conclusions were consistent with this hypothesis, suggesting that living with myofascial face pain contributes to the elevated rate of depression. On the other hand, a more recent study investigating the comorbidity of fibromyalgia (FM) and PTSD produced an alternative interpretation for the interaction between chronic pain and anxiety.³² In this study, surveys were conducted among community-dwelling women before and after the 9/11 attack in New York City. The odds of probable PTSD were more than 3 times greater in women with FM-like symptoms than those without, assessed after 9/11. The OR was not reduced after controlling for FM-like symptoms before 9/11 or for the potentially confounded symptoms of PTSD specifically related to arousal. As mentioned, most of this research is now 10 to 20 years old, and some of these conceptualizations are certainly due for an update.

In some ways, it may not be important to know which came first, pain or depression or anxiety, in the early history of the events observed. Instead, an understanding of how this pattern of suffering is maintained and worsened, on a day-to-day basis, may be more practical. This effort should perhaps include identifying the circumstances that give rise to these behavioral patterns, and the most manipulable elements in the patients’ experiences, where impacts on these are most likely to lead to significant and durable improvement in functioning and well-being.