Eisenberg and colleagues estimated that Americans made approximately 425 million visits to CAM practitioners in 1990, more than the total number of visits to primary care physicians during that period . A large-scale follow-up study showed that CAM use among the general public increased from 34% in 1990 to 42% in 1997 . By 2001, hospitals that offered CAM services were citing patient demand as a primary motivating factor . CAM is emerging as an important form of care.
The National Center for Complementary and Alternative Medicine (NCCAM) defines Complementary and Alternative Medicine (CAM) as "a group of diverse medical and health care systems, practices, and products that are not presently considered to be part of conventional medicine" . This definition, arrived at after much debate , demonstrates that the scope of CAM can be quite large and dynamic. The American Cancer Society separately defines "complementary" and "alternative." "Complementary" methods are supportive methods used to complement evidence-based treatment. Complementary therapies do not replace mainstream cancer treatment and are not promoted to cure disease. Rather, they control symptoms and improve well-being and quality of life. Alternative methods are defined as unproved or disproved methods, rather than evidence-based or proven methods to prevent, diagnose, and treat cancer .
Within the epidemiological literature on CAM use, variations in the definition of CAM, study populations and methodologies make it very difficult to compare studies and reach firm conclusions. These difficulties notwithstanding, it is apparent that CAM use continues to be significant. A survey developed by NCCAM and the National Center for Health Statistics (NCHS) conducted in 2002 revealed that 36% of US adults had used some form of CAM in the year prior to the survey. When prayer for health-related purposes was included in the definition of CAM, the prevalence rose to 62% .
Some experts suggest that CAM use is predictably increased in situations such as cancer, where "illness consequences are high and beliefs in the effectiveness of conventional treatments (i.e. response efficacy) are low" . Indeed, several studies have shown that cancer patients are increasingly incorporating complementary therapies into their overall treatment [8, 9]. In one systematic review of the use of CAM among patients with cancer, the reported prevalence rate ranged from 7 to 64% . In 2001, an update from NCCAM pointed out that among cancer patients, the use of CAM ranges between 30 and 75% worldwide . Even higher rates, ranging from 67% to 83% have been documented in patients with breast cancer [11, 13]. At a comprehensive cancer center, when CAM was broadly defined to include spiritual practices and psychotherapy, 83.3% of subjects had used at least one CAM approach .
Chronic pain is also an area where CAM use has flourished. In 1997, researchers found that 54% of Americans who reported back or neck pain in the previous 12 months had used complementary therapies to treat their condition. At that time, chiropractic therapy was the most common "unconventional" therapy used in the United Sates . The more recent NCCAM/NCHS survey  supports these findings from 1997, indicating that CAM approaches are very often used to treat body pain, especially in the back and neck. This survey also revealed CAM use is greater among certain groups such as women, those with higher education, those who had been hospitalized within the previous year, and former smokers.
In keeping with the trend toward increased support of CAM use, the Department of Veterans Affairs Health Care Programs Enhancement Act of 2001 required the Veterans Administration (VA) Health Care System to provide chiropractic programs nationwide . However, little is known about the use of CAM or patient demand for such services within the VA, which manages the largest integrated healthcare system in the US.
Data on CAM use in veterans is limited to one geographic location in Southern Arizona where CAM use may be influenced by a high level of advertisement and promotion [13, 14]. In this location, 49.6% of veterans reported current or previous use of CAM.
The primary purpose of this study was to ascertain the prevalence of 6 common CAM treatments and determine characteristics associated with their use among veterans whose CAM use was expected to be high, those receiving care at the oncology and chronic pain clinics . We hypothesized that CAM use would be lower than that of the general population and would be influenced by income, educational level, insurance status, diagnosis [2, 8, 20] and beliefs about the cause of illness [21, 22]. National surveys show women are more likely to utilize CAM than men ; as such, we expected to find low prevalence of CAM use among our predominantly male veteran population. We also hypothesized that CAM use among veterans who received additional care outside the VA would be higher than use among veterans who received care only at the VA because seeking care outside the VA is correlated with higher income[15, 16]