For how we live.
Across 29 studies the overall effect on chronic back pain was not significant. Split by whether the current was strong enough to be clearly felt, one subgroup showed a large effect and the other none.
Cochrane found a clinically important 15.2-point pain reduction across 249 trials. A reanalysis excluding trials with fewer than 70 participants put the effect below the threshold that counts as meaningful.
The gap between those two numbers is the whole argument. An individual-patient meta-analysis of 20,827 people found real effects on both comparisons, and found that the choice of sham changed the answer.
Analgesic trials keep failing, and one reason is that the comparison arm keeps improving. Where a trial recruits, how long it runs and how big it is all move the placebo response — and none of that is about the drug.
A network meta-analysis found six treatments clearing the clinically important threshold in the short term. It also graded 98.6% of the evidence very low certainty, and found nothing that held up past a year.