While doctors around the world for years have recommended that patients experiencing back pain take acetaminophen (e.g. Tylenol), a new study out Wednesday shows that the drug works no better than a placebo. “Our result illustrates the problems in relying on that indirect evidence when setting guidelines,” said Christopher M. Williams, a researcher at the George Institute for Global Health in Sydney and lead author of the study. Roughly two-thirds of adults experience back pain. The three-month study that included 1,643 people showed no differences between those taking the drug and those taking the placebo in terms of recovery time, pain, quality of life, as well as other measures.