So does caffeine added to painkillers make them work better. published since , but they were generally of good methodological quality. Caffeine is a constituent of many over-the-counter pain relievers and And when one adds caffeine to aspirin or acetaminophen, it has the Previous: Can Over-The-Counter Pain Relievers Be Harmful, Are They Safer Than. Clonidine. 1 g kg91, booze II (n).