Despite wide use in clinical practice, acupuncture remains a controversial treatment
for chronic pain. Our objective was to update an individual patient data meta-analysis
to determine the effect size of acupuncture for 4 chronic pain conditions. We searched
MEDLINE and the Cochrane Central Registry of Controlled Trials randomized trials published
up until December 31, 2015. We included randomized trials of acupuncture needling
versus either sham acupuncture or no acupuncture control for nonspecific musculoskeletal
pain, osteoarthritis, chronic headache, or shoulder pain. Trials were only included
if allocation concealment was unambiguously determined to be adequate. Raw data were
obtained from study authors and entered into an individual patient data meta-analysis.
The main outcome measures were pain and function. An additional 13 trials were identified,
with data received for a total of 20,827 patients from 39 trials. Acupuncture was
superior to sham as well as no acupuncture control for each pain condition (all P < .001)
with differences between groups close to .5 SDs compared with no acupuncture control
and close to .2 SDs compared with sham. We also found clear evidence that the effects
of acupuncture persist over time with only a small decrease, approximately 15%, in
treatment effect at 1 year. In secondary analyses, we found no obvious association
between trial outcome and characteristics of acupuncture treatment, but effect sizes
of acupuncture were associated with the type of control group, with smaller effects
sizes for sham controlled trials that used a penetrating needle for sham, and for
trials that had high intensity of intervention in the control arm. We conclude that
acupuncture is effective for the treatment of chronic pain, with treatment effects
persisting over time. Although factors in addition to the specific effects of needling
at correct acupuncture point locations are important contributors to the treatment
effect, decreases in pain after acupuncture cannot be explained solely in terms of
placebo effects. Variations in the effect size of acupuncture in different trials
are driven predominantly by differences in treatments received by the control group
rather than by differences in the characteristics of acupuncture treatment.