In a small randomized study of 44 subjects, in which one author disclosed a proprietary interest in Vax-D, it was shown to have a clinical success rate of 68.4%.

A 2004 report by the State of Washington Department of Labor and Industries concluded "Published literature has not substantially shown whether powered traction devices are more effective than other forms of traction, other conservative treatments, or surgery."A 2005 review of VAX-D (including the Sherry study above) by the Workers' Compensation Board of British Columbia concluded "To date there is no evidence that the VAX-D system is effective in treating chronic LBP associated with herniated disc, degenerative disc, posterior facet syndrome, sciatica or radiculopathy."

A 2006 systematic review of studies of spinal decompression using motorized traction devices conducted between 1975 and October 2005 (including the two mentioned above) concluded that "...the efficacy of spinal decompression achieved with motorized traction for chronic discogenic low back pain [remained] unproved", and called for "Scientifically more rigorous studies with better randomization, control groups, and standardized outcome measures … to overcome the limitations of past studies." A technology assessment conducted in 2007 by the Agency for Healthcare Research and Quality (for which the two studies cited above were included for analysis) said "Currently available evidence is too limited in quality and quantity to allow for the formulation of evidence-based conclusions regarding the efficacy of decompression therapy as a therapy for chronic back pain when compared with other non-surgical treatment options."

A 2007 critique of research studies, including the two cited above, said:

There is very limited evidence in the scientific literature to support the effectiveness of non-surgical spinal decompression therapy. This intervention has never been compared to exercise, spinal manipulation, standard medical care or other less expensive conservative treatment options which have an ample body of research demonstrating efficacy. Considering the cost-benefit relationship, many better researched and less expensive treatment options are available to the clinician.