Opioid-mediated placebo responses boost pain endurance and physical performance: is it doping in sport competitions?

Abstract

The neurobiological investigation of the placebo effect has shown that placebos can activate the endogenous opioid systems in some conditions. So far, the impact of this finding has been within the context of the clinical setting. Here we present an experiment that simulates a sport competition, a situation in which opioids are considered to be illegal drugs. After repeated administrations of morphine in the precompetition training phase, its replacement with a placebo on the day of competition induced an opioid-mediated increase of pain endurance and physical performance, although no illegal drug was administered. The placebo analgesic responses were obtained after two morphine administrations that were separated as long as 1 week from each other. These long time intervals indicate that the pharmacological conditioning procedure has long-lasting effects and that opioid-mediated placebo responses may have practical implications and applications. For example, in the context of the present sport simulation, athletes can be preconditioned with morphine and then a placebo can be given just before competition, thus avoiding administration of the illegal drug on the competition day. However, these morphine-like effects of placebos raise the important question whether opioid-mediated placebo responses are ethically acceptable in sport competitions or whether they have to be considered a doping procedure in all respects.

Figure 1.

Experimental simulation of the competition. The precompetition training, the competition day, and the postcompetition control are shown for each group.

Figure 2.

A–D, Mean pain endurance times (±SD) in the precompetition training phase, on the day of competition, and in the postcompetition control. It can be seen that, on the day of competition, a significant increase in performance occurred after placebo administration compared with baseline in both groups B and C, whereas in group A and D, no increase in performance occurred. The performance of team C was significantly better than that of group B.

Figure 3.

The correlation between the percentage increase in performance after the first and second injection of morphine and the percentage increase in performance after placebo in group C and D. A correlation was present after placebo administration in group C, and this correlation was modified by naloxone in group D.