Itoh 1980.

Methods	Double‐blind, head‐to‐head comparison, natural colds
Participants	184 adults, mean age, sex not reported for the subgroup of colds, 29 centres, outpatient departments of hospitals and clinics, URTI onset ≤ 3 days
Interventions	2 groups: ketoprofen 50 mg 3 times and aspirin 500 mg 3 times for 3 days
Outcomes	No significant difference in FGIR between 2 groups
Notes	No available data on adverse effects for the subgroup of common colds
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Comment: insufficient information about the sequence generation process
Allocation concealment (selection bias)	Low risk	"... randomisation process was done by two controllers and key codes were kept by controllers (in Japanese)" Comment: probably done
Blinding (performance bias and detection bias) All outcomes	Low risk	"... double‐blind method...active drug capsule and aspirin capsule were quite similar in shape (in Japanese)" Comment: probably done
Incomplete outcome data (attrition bias) All outcomes	Low risk	"91/93 cases in ketoprofen group and 89/91 cases in aspirin group were finally analyzed" Number of withdrawals was too small to make any important difference to the estimated intervention effect Comment: probably done
Selective reporting (reporting bias)	Unclear risk	No protocol, no convincing text
Other bias	Low risk	The study appears to be free of other sources of bias