Time-varying magnetic and electromagnetic fields, and the family where the evidence gradient is starkest. Two members are real, dosed, regulator-cleared mechanisms — PEMF (classical induction, narrow orthopedic / neuropsychiatric clearances) and TTFields (intermediate-frequency alternating fields that disrupt tumour-cell mitosis, with a positive phase III survival trial). The rest is the historical “frequency-medicine” tradition (Lakhovsky's wave oscillator, the Mishin coil) whose hardware is ordinary but whose curative claims contradict physics. The surface resemblance — “tuned EM frequencies act on cells” — is exactly what makes the contrast instructive: a defined dose, target, and trial on one side; an undefined doctrine on the other.