Believing you are taking caffeine could improve sports performance, but the evidence remains weak

What the researchers compared

The review brings together 17 studies in which healthy adults received a placebo falsely described as caffeine. The performance tests included bench presses, cycling time trials and repeated sprints.

The analysis compares performance under this placebo with baseline measurements. It therefore seeks to estimate the effect associated with believing you have received caffeine, rather than the substance’s pharmacological effect. The available abstract specifies neither the total number of participants nor the duration of the different experiments.

A favorable average effect, not a percentage improvement

The pooled effect favors the placebo presented as caffeine. The standardized mean difference is 0.49, with a 95% confidence interval ranging from 0.28 to 0.69. The authors describe this effect as small to moderate.

This measure allows results expressed on different scales to be combined. It does not represent a percentage improvement and cannot establish a precise gain in seconds, power or repetitions. An average pooling several tests also does not predict the benefit for an individual athlete.

Biases that limit the conclusion

Nine studies are judged to have a high risk of bias, and eight have an unclear risk. None is therefore classified as low risk. The GRADE assessment rates the overall quality of the evidence as low, despite a statistically favorable pooled result.

The authors call for more rigorous experiments, particularly with researchers blinded to the treatment administered and better concealment of group allocation. These precautions help limit the influence of expectations and the way the experiment is conducted on the results.

What this means for interpretation

This review suggests that expectations related to caffeine may contribute to observed performance. It cannot determine how much of the benefit of actual caffeine is attributable to these expectations.

Nor does it test a strategy of deliberately taking a placebo while knowing what it contains. Turning these findings into practical advice would therefore go beyond what the data show.

What we can take away

Believing you are receiving caffeine could improve some aspects of sports performance. However, the methodological weaknesses of the studies prevent this from being considered a reliable strategy or a proven substitute for caffeine.