Comparison 1.

Aspirin 900 mg or 1000 mg versus placebo

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Headache relief at 2 hours	6	2027	Risk Ratio (M-H, Fixed, 95% CI)	1.64 [1.48, 1.83]
2 Pain free at 2 hours	6	2027	Risk Ratio (M-H, Fixed, 95% CI)	2.08 [1.70, 2.55]
3 Headache relief at 1 hour	4	1288	Risk Ratio (M-H, Fixed, 95% CI)	2.41 [1.96, 2.96]
4 24-hour sustained headache relief	3	1142	Risk Ratio (M-H, Fixed, 95% CI)	1.63 [1.37, 1.95]
5 Pain free at 2 hours - effect of formulation	6		Risk Ratio (M-H, Fixed, 95% CI)	Subtotals only
5.1 Soluble	4	1230	Risk Ratio (M-H, Fixed, 95% CI)	1.92 [1.51, 2.44]
5.2 Tablet	2	797	Risk Ratio (M-H, Fixed, 95% CI)	2.47 [1.70, 3.58]
6 Headache relief at 2 hours - effect of formulation	6		Risk Ratio (M-H, Fixed, 95% CI)	Subtotals only
6.1 Soluble	4	1230	Risk Ratio (M-H, Fixed, 95% CI)	1.65 [1.43, 1.89]
6.2 Tablet	2	797	Risk Ratio (M-H, Fixed, 95% CI)	1.64 [1.38, 1.95]
7 Relief of associated symptoms at 2 hours	6		Risk Ratio (M-H, Fixed, 95% CI)	Subtotals only
7.1 Nausea	4	878	Risk Ratio (M-H, Fixed, 95% CI)	1.26 [1.10, 1.44]
7.2 Vomiting	3	139	Risk Ratio (M-H, Fixed, 95% CI)	1.12 [0.94, 1.34]
7.3 Photophobia	5	1236	Risk Ratio (M-H, Fixed, 95% CI)	1.37 [1.20, 1.56]
7.4 Phonophobia	5	1217	Risk Ratio (M-H, Fixed, 95% CI)	1.44 [1.27, 1.64]
8 Persistence of associated symptoms after 2 hours	6		Risk Ratio (M-H, Fixed, 95% CI)	Subtotals only
8.1 Nausea	4	1446	Risk Ratio (M-H, Fixed, 95% CI)	0.79 [0.68, 0.93]
8.2 Vomiting	3	1182	Risk Ratio (M-H, Fixed, 95% CI)	0.77 [0.43, 1.37]
8.3 Photophobia	5	1639	Risk Ratio (M-H, Fixed, 95% CI)	0.79 [0.72, 0.87]
8.4 Phonophobia	5	1639	Risk Ratio (M-H, Fixed, 95% CI)	0.75 [0.68, 0.84]