Delay Erases the Pain Relief From an Open-Label Placebo, Trial Finds

In a small randomized trial of people with chronic jaw and facial pain, a placebo given openly as inert relieved pain only when it started right away; the same placebo, withheld for 45 days, worked no better than no treatment at all.

Delaying an open-label placebo, a treatment openly identified to patients as inert, erased its pain-relieving effect in a randomized trial of people with temporomandibular disorder (TMD), a chronic jaw and facial pain condition, according to a study in The Journal of Pain. Patients who began the placebo immediately reported lower pain than those whose placebo was withheld for the same period, the trial found; the delayed group's early pain scores did not differ from a group given no placebo at all.

Open-label placebo, unlike the deceptive kind used in classic drug trials, tells patients plainly that the pill or treatment contains no active ingredient; earlier trials in low back pain, migraine and irritable bowel syndrome have still recorded symptom improvement. What had not been tested directly, the researchers wrote, is whether the moment placebo administration begins, relative to the onset or duration of pain, changes whether it works at all. To test that, they randomized 50 TMD patients into three arms over three months: one group (17 people) received the placebo for the first 45 days then stopped; a second group (18 people) went 45 days with no treatment before starting the placebo; and a comparison group of 15 people received no placebo and was simply monitored throughout, using daily diary ratings collected through ecological momentary assessment.

A linear mixed model found a significant overall difference in pain intensity across the three groups (F(2,45.04)=6.44, p=0.003). The group that started the placebo right away reported significantly lower pain than the delayed group (p=0.008) and lower than the untreated comparison group (p=0.011); critically, during the delay period the delayed group's pain scores were statistically indistinguishable from the untreated group (p=1.000), the paper reported. Once the delayed group finally began the placebo in the second phase of the trial, pain intensity did drop compared with their own untreated period, and the immediate-start group's pain relief persisted for a time even after that group's placebo was stopped, a pattern the authors described as evidence that timing, not just belief in inert treatment, shapes whether an open-label placebo produces measurable analgesia.

The findings add a temporal wrinkle to a growing research literature on non-deceptive placebo effects, one that researchers say may matter for how future open-label placebo trials are designed and timed, rather than for anything a patient or family should act on directly.