This study aimed at comparing the time courses of pain relief in tension headache after taking 648 mg solid ASA and after taking 648 mg effervescent ASA (acetyl salicylic acid). A modified double dummy technique with both solid and effervescent placebo was used. 47 patients entered, and 33 patients took all four trial drugs. No statistically significant difference between solid and effervescent ASA could be demonstrated. ASA was significantly better than placebo although the median rating of ASA in this study was unexpectedly poor - as was the placebo response. This fact might have reflected the severely afflicted nature of a headache clinic's population.

Different pain rating scales are compared, and it is concluded that the overall (GLOBAL) rating is sensitive, but should not be used alone, since it may sometimes reflect less relevant factors. The power of the trial was good, but reflects the comparatively poor responsiveness to ASA (low variance) in this particular patient population. An advantage of the effervescent preparation in more ASA-responsive patients cannot be ruled out. It is advised for future studies to recruit patients from general practice rather than from a headache-clinic population.