This randomised, double-blind, placebo-controlled trial enrolled 1,028 adults presenting to the emergency department with acute non-traumatic headache. All received 1 g of oral paracetamol before randomisation, then either 2 g of intravenous magnesium sulphate in 150 mL of saline or saline alone, infused over 30 minutes.
Treatment success, defined as at least a 30% reduction in numerical rating scale at 30 minutes, occurred in 78.9% with magnesium against 65.1% with placebo (difference 13.8%, 95% CI 8 to 19). However, the actual pain-score differences at every measured time point fell below 1.3 points, the accepted threshold for clinical importance. Rescue analgesia was needed less often, in 7.1% against 15.3% (difference -8.2%, 95% CI -12 to -4.3), satisfaction was higher at 91.7% against 85.1%, and adverse events were more common at 15.4% against 11.1%.
The two framings of the same trial point different ways, and the resolution is in the secondary outcomes. A responder analysis and a mean pain score can disagree when a treatment helps some patients substantially and others not at all, and here the halving of rescue analgesia suggests genuine benefit rather than a statistical artefact. Magnesium is cheap and familiar. This supports it as a reasonable adjunct after simple analgesia in a department that already stocks it, not as a new standard.
- Treatment success 78.9% vs 65.1% (difference 13.8%)
- All pain-score differences below the 1.3-point clinical threshold
- Rescue analgesia halved: 7.1% vs 15.3%
- Mild adverse events more common: 15.4% vs 11.1%
The statistics, in plain English
This trial shows why a p-value alone settles nothing. With over a thousand patients, a difference far too small for any individual to notice will still be statistically significant, which is exactly what happened to the pain scores. The 1.3-point threshold exists because that is roughly the smallest change patients report as meaningful. The rescue-analgesia difference, 7.1% against 15.3%, is the outcome that survives that test, because needing another drug is a real event rather than a point on a scale.
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