Radiesthesia has not generally been tested as a distinct discipline in its own large-scale trials, but because it shares dowsing's exact claimed mechanism, an unexplained physical sensitivity manifested as an involuntary hand or pendulum movement, the extensive controlled testing done on dowsing applies directly to it. The largest and most rigorous such test remains the Munich dowsing trials of the late 1980s, in which physicists tested more than five hundred self-identified dowsers across more than ten thousand individual trials, asking them to detect a concealed water pipe under blinded, controlled conditions; the dowsers performed at a level consistent with chance, with no participant demonstrating reliable accuracy across repeated attempts. Comparable blinded tests of pendulum-based diagnosis specifically, asking radiesthesists to identify a known medical condition, contaminated sample, or similar target without any sensory cue, have likewise found no accuracy beyond chance.
The consistent explanation offered by researchers for why the pendulum nonetheless appears to move meaningfully is the ideomotor effect, first demonstrated in a related context by Michael Faraday's 1853 investigation of table-turning, in which he showed that participants' own small, unconscious muscular movements, driven by expectation, were sufficient to produce apparently independent motion without any external force. Because radiesthesia involves no substance or physical intervention, it carries no direct toxicity or injury risk in itself; its documented harm is entirely indirect, arising in the minority of cases where a pendulum-based health assessment substitutes for, or delays, a properly conducted medical diagnosis.