Cayenne pepper / capsicum

That cayenne pepper poured into a wound or taken in water stops bleeding almost instantly, halts a heart attack in progress, and heals stomach ulcers rather than aggravating them.

Popularised by American herbalist John Christopher and later by Richard Schulze, whose lecture claim that he "never lost a patient" to a heart attack because of cayenne tincture is the source of most versions circulating today. The claim spread through naturopathic teaching, prepper and off-grid communities, and now short-form video.

Capsaicin is a real vasoactive compound with real pharmacology, and topical capsaicin is an approved treatment for neuropathic pain. That is where the evidence stops. There is no clinical evidence that cayenne stops haemorrhage; direct pressure does, which is why a wound treated with cayenne and pressure appears to work. For ulcers the picture is genuinely mixed rather than settled: some studies suggest chilli consumption is not the ulcer-causer folk wisdom assumed, and a few suggest a protective association, but none establish cayenne as a treatment. No evidence supports it for heart attack, where every minute before reperfusion costs heart muscle.