The analgesic effects of caffeine in headache.

Caffeine is frequently added to mild analgesic preparations but its effect when used alone on pain has never been studied in humans. Using a double-blind placebo-controlled multiple crossover design, 53 patients with non-migrainous headaches were given placebo, acetaminophen, 2 doses of caffeine and 2 combinations of caffeine with acetaminophen. Caffeine appeared to have independent analgesic effects that were equivalent to acetaminophen and were still significant when statistical adjustments were made for prior caffeine consumption and caffeine's effects on mood.