Two-thirds of adults experience back pain sometime during their lives, and most take acetaminophen, found in brands like Tylenol and Panadol, for relief. But new research has found that those medicines are no more helpful than swallowing a sugar pill.

A study published this week in a medical journal called The Lancet split 1,643 people with acute low-back pain into three groups, each given two boxes. One group received two boxes of 500-miligram acetaminophen tablets, with instructions to use the second box “as needed’; the second group got a box of acetaminophen and an as-needed box of placebos; and the third group received two boxes of placebos. Researchers told the participants to take six tablets per day from the regular box and up to two from the as-needed box.

Over the course of three months, the researchers found no difference among the three groups. Subjects showed no variation in terms of pain, recovery time, function, disability, symptom change, sleep or quality of life. About 75% of the participants were happy with their results, whether or not they had received the placebos.

Write to Eliana Dockterman at eliana.dockterman@time.com.