Not all placebos are equal in knee osteoarthritis

(HealthDay)—Not all placebos are equally effective for knee osteoarthritis and some can trigger clinically relevant responses, according to a review published online July 28 in the Annals of Internal Medicine.

Raveendhara R. Bannuru, M.D., Ph.D., from Tufts University in Boston, and colleagues examined the effects of alternative placebo types on pain outcomes in knee osteoarthritis. Data were included from 149 randomized trials of adults with knee osteoarthritis that reported pain outcomes. The trials compared widely used pharmaceuticals against four placebos: oral, intra-articular, topical, and oral plus topical.

The researchers found that based on a network meta-analysis with four separate placebo nodes (differential model), intra-articular placebo and topical placebo had significantly greater effect sizes than oral placebo (effect sizes, 0.29 and 0.20, respectively). Compared with a network model that considered all placebos equivalent, the differential model showed marked differences in the relative efficacies and hierarchy of the active treatments. For pain reduction, intra-articular and topical therapies were superior to oral treatments in the model accounting for differential effects. Oral nonsteroidal anti-inflammatory drugs were superior when these effects were ignored.

"Differential placebo effects can substantially alter estimates of the relative efficacies of active treatments, an important consideration for the design of clinical trials and interpretation of the results," the authors write.

Several authors disclosed financial ties to the pharmaceutical industry.