The placebo and nocebo effect in sport: intentions, attitudes and beliefs towards sport supplements and banned performance enhancing substances

The focus of this research is to determine the magnitude and moderators of placebo and nocebo effects on sport performance and to explore the impact of a placebo intervention on athletes’ beliefs and intentions towards sport supplements. Recent research suggests that supplement users may be more likely to use banned substances (i.e. doping) and that beliefs and intentions towards supplements may influence future supplement use. As such, this research also explores the effects of a placebo intervention on athletes’ attitudes to doping.

Study 1 focuses on the development and validation of the Sports Supplements Beliefs Scale. This measure is used to assess athletes’ beliefs about sport supplements and the impact of the placebo intervention conducted in Study 2 on these beliefs.

Study 2 uses a placebo intervention to examine the magnitude and moderators of the placebo and nocebo effect on repeat sprint performance, and Study 3 examines the impact of this intervention on participants’ beliefs and intentions to use sport supplements and attitudes to doping. In Study 2, no significant mean placebo effect on sport performance was evident, however, a significant mean nocebo effect compared to no treatment controls was observed. Further analyses indicated that participants’ intentions to use sport supplements influenced the direction and magnitude of the placebo effect.

Study 3 showed that participants’ beliefs and intentions towards sport supplements and attitudes to doping changed after the intervention. Although it appeared to reduce the likelihood of athletes using sport supplements and banned substances overall, participants that were not intending to use sport supplements before the intervention were more likely to use them after.

In conclusion, data from this research suggest that an athlete’s intention to use sport supplements moderates the direction and magnitude of placebo effects on sport performance and that a placebo intervention significantly influences athletes’ beliefs and intentions towards sport supplements and attitudes to doping. These results have important implications for how international and national anti-doping organisations develop their anti-doping education interventions. Interventions aimed at educating athletes about the placebo effect and targeting their use of sport supplements, may prevent future doping behaviours.