Caffeine as an analgesic adjuvant. A double-blind study comparing aspirin with caffeine to aspirin and placebo in patients with sore throat. Despite its frequent clinical use in analgesic agents, caffeine has not been accepted unequivocally as an analgesic adjuvant. To evaluate this activity of caffeine, we used new study methods in a randomized controlled trial on patients with acute sore throat due to tonsillopharyngitis. Patients were randomly assigned to receive a single dose of one of three treatments: 800 mg of aspirin with 64 mg of caffeine (n = 70), 800 mg of aspirin (n = 68), or placebo (n = 69). Under double-blind conditions, during a 2-hour evaluation period, patients used different rating scales to assess pain intensity, change in pain, relief, and two qualities of throat pain, how swollen the throat felt, and difficulty swallowing. Aspirin with caffeine and aspirin alone were significantly more effective than placebo for all efficacy measurements from 30 minutes through 2 hours and overall. The aspirin-caffeine combination also showed evidence of activity at 15 minutes on the relief scale. Aspirin with caffeine was more effective than aspirin alone after 30 minutes and over the entire study period. For patients with fever, both active treatments were equally effective antipyretic agents. We conclude, therefore, that 800 mg of aspirin, given alone or with 64 mg of caffeine, is an effective analgesic and antipyretic agent. Because the aspirin-caffeine combination is significantly more effective than aspirin alone as an analgesic, we also conclude that 64 mg of caffeine is an analgesic adjuvant. 