Placebo disclosure does not result in negative changes in mood or attitudes towards health care or the provider.

Objectives : The purposes of this study were to (1) determine whether disclosure of having received a placebo treatment following participation in a randomized manual therapy trial resulted in changes in negative mood or attitudes towards health care and the provider and (2) examine the association between changes in mood or attitude and changes in clinical outcomes over the two-week study period. Methods : Participants with low back pain ( N  = 110) were randomly assigned to receive a spinal manipulative therapy (SMT), a standard placebo SMT in which participants were aware of a chance of receiving a placebo, an enhanced placebo SMT in which participants were instructed 'the manual therapy technique you will receive has been shown to significantly reduce low back pain in some people,' or no treatment. Outcomes included pain (Numeric Rating Scale), disability (Oswestry Disability Index), and negative mood and attitudes towards health care and the provider (visual analog scales). Pain and disability were obtained at baseline and two weeks. Mood and attitude measures were assessed at baseline, at the start of the final session, and upon completion of the final session following disclosure of group assignment. Results : Disclosure of having received a placebo treatment was not associated with worsening of mood or attitudes towards health care or the provider ( p  > 0.05). A small, but significant ( p  < 0.05) association was observed between two-week changes in disability and immediate changes in mood ( r  = 0.31-0.36) upon disclosure of having received a placebo. This analysis indicates an association between larger improvements in disability and more positive changes in mood. Discussion : Placebo treatment use in clinical practice is common yet controversial due to the deceptive nature. Our findings suggest disclosure of having received a placebo treatment is not associated with adverse changes in negative mood or attitudes towards health care or the provider.