The Free Enterprise Radon Health Mine is the oldest of the bunch, opening for business as Montana's first uranium mine in 1949, before transitioning its extraction focus to the more intangible resource of personal health just three years later.
“Radon therapy,” the Free Enterprise brochure explains, simply “consists of series of daily visits to the Mine,” where levels of the colorless, odorless, tasteless, and highly radioactive gas fluctuate between 700 to 2,200 picoCuries per liter of air. On average, they are about 1700 pC/l.
By way of contrast, the U.S. Environmental Protection Agency, which regards radon as a toxic carcinogen, classifies levels of 4 pCi/L or above as the “action point,” at which homeowners should take steps to limit their exposure. In the eyes of the World Health Organization, radon inhalation is the second largest cause of lung cancer in the world. In the United States, it is responsible for about 21,000 deaths from the disease every year, according to EPA estimates.
Hence the somewhat niche appeal of radon therapy, at least in the United States. The American Medical Association roundly denounced it as quackery in the 1950s, and has not reconsidered its stance since. Elsewhere, particularly in central Europe, Russia, and Japan, radon therapy for arthritis relief is an established alternative medicine—despite the fact that no one knows quite how it works.