Which conditions show the strongest benefit over sham/placebo?

The short version: the biggest sham-controlled effects are in burning mouth syndrome, fibromyalgia fatigue, and hair density, but the certainty behind them is only moderate.

An umbrella review of 15 meta-analyses covering 204 randomized trials and over 9,000 people found 12 significant effects, and not one reached high certainty [1]. Five endpoints hit moderate certainty: burning mouth pain, knee arthritis disability, fibromyalgia fatigue, hair density in pattern baldness, and cognitive function [1]. The rest, including temporomandibular joint pain and tendinopathy pain, were low or very low certainty [1].

Effect size here is a standardized number: bigger means a larger gap versus sham. The burning mouth signal is the most consistent, but the underlying trials are small, use inconsistent laser settings, and follow people only briefly [2]. Several of those trials found no clear edge over placebo at all [2]. The umbrella review itself calls for standardized protocols and better trials, which tells you the field knows its own evidence is shaky [1].

The wound-healing records are weaker still: one is in diabetic rats [3], and the human diabetic foot ulcer trial compared laser plus standard care to standard care alone, not to a sham light [4]. That design cannot separate the light from the attention.

My call: burning mouth syndrome has the best sham-controlled case, with fibromyalgia fatigue and hair density close behind, all at moderate certainty only. Confidence: moderate.