Signalling questions	Description	Response options
3.1 Were data for this outcome available for all, or nearly all, participants randomized?	180 were equally randomized to caffeine or placebo cross‐over arms We excluded from analysis participants who later withdrew from the study (three randomized to placebo, two to caffeine) or did not adequately abstain from caffeine (baseline caffeine levels in the study periods differed by ≥1 μg/mL (two randomized to placebo and five to caffeine). A flowchart is presented in Figure 2	Y
3.2 If N/PN/NI to 3.1: Is there evidence that the result was not biased by missing outcome data?		NA
3.3 If N/PN to 3.2: Could missingness in the outcome depend on its true value?		NA
3.4 If Y/PY/NI to 3.3: Do the proportions of missing outcome data differ between intervention groups?		NA
3.5 If Y/PY/NI to 3.3: Is it likely that missingness in the outcome depended on its true value?		NA
Risk‐of‐bias judgement		Low

Note: N, No; NI, No Information; PN, Probably No; PY, Probably Yes; Y, Yes.