A snake-stone, also known as a viper's stone, black stone, schwarze Steine, pierres noire, piedritas negras or serpent-stone, is an animal bone or stone used as folk medicine for snake bite in Africa, South America, and Asia.
The early Celtic era European Adder stone is also called a snake stone, and is usually made from coloured glass, often with holes. Its purpose is for protection against evil spirits rather than snake bite.
Dr. Linnea Smith from the Yanamono Medical Clinic in the remote Amazon basin of northeastern Peru wrote 
- The black stone is a fondly held concept in our area, where snakebites are common and sometimes fatal. ... when one lives far from ambulances, med-flights, hospitals, doctors, and when one is confronted with a potentially lethal problem, anything seems better than nothing. Personally, I’d rather have antivenom. Then again, if nothing else is available, what is one to do? And placebo effect is undoubtedly real. ... In any case, better that a person stricken by a snake have some hope than feel completely without recourse...
Experts are concerned that relying on a black stone may prevent snakebite victims from seeking appropriate medical help. No scientific study has shown that black stones per se are effective, but, most guidelines for snakebite first-aid stress the need for keeping the victim calm (because acute stress reaction increases blood flow and endangers the victim, and panic is infectious and can compromise judgment).
Accounts differ widely on how to make and use a 'black stone'.
Dr. Linnea Smith reports that, in Peru, a black stone is a small charred cow bone, "applied to the site of a poisonous snakebite and tied firmly in place. It is left there for several days, during which time it supposedly draws the venom from the wound. Once the poison is all removed, the ‘stone’ loosens of its own accord and falls off. ... despite the fact that the state nursing course book admits that no evidence has ever been produced to document the effectiveness of the black stone, each student is required to make ... one ... as a part of the first aid module."
Persian/Iranian writer Kazwini describes the snake-stone as being the size of a small nut. An injury inflicted by a venomous creature is to be immersed in warm water or sour milk. The snake-stone is then dropped into the liquid to supposedly draw out the poison.
The steps suggested in an African leaflet are:
- Choose a large dry cow thigh bone
- Cut it into small pieces
- Smooth them with sandpaper
- Wrap the pieces in foil
- Place in a charcoal fire for 15 to 20 minutes
Views on snake-stones expressed in scientific studies
A Nigerian study recommended "education on the need to avoid the use of popular first aid measures of doubtful benefit." The same doctors later reported that Black Stones may be beneficial, but "those who used the black stone required significantly higher quantity of antivenom as compared to those that used the tourniquet". In their report they noted slightly higher tissue necrosis in patients who use tourniquets, but this was not (statistically) significant; other scientists have recommended against tourniquets (see treatment of snakebites and outdated treatments).
An Indian study stated, "unscientific methods like ‘black stone’ healing contribute to the delay in seeking appropriate medical care."
- Wereld-Missiehulp. "BLACKSTONES" (in Dutch). Retrieved 2007-03-06. Archived April 2, 2015, at the Wayback Machine.
- JKA Madaki; RE Obilom; BM Mandong (2005). "Pattern of First-Aid Measures Used by Snake-bite Patients and Clinical Outcome at Zamko Comprehensive Health Centre, Langtang, Plateau State". Nigerian Medical Practitioner. 48 (1). Retrieved 2010-10-15.
- BBC News (2005-05-02). "Search for a snakebite cure". Retrieved 2007-03-06.
- Tagne, Jean-Bruno. "Pierre noire : Cet aspirateur de venins / Black Stone: This vacuum cleaner of venoms" (in French). Retrieved 2007-03-06.
- B. Adhisivam; S. Mahadevan (2006). "Snakebite Envenomation in India: A Rural Medical Emergency". Indian Pediatrics. 43 (6): 553–4. PMID 16820669. Retrieved 2010-10-15.
- Dr. Linnea Smith. "Piedra Negra" (PDF). Retrieved 2007-03-07.
- CongoForum. "La pierre noire et son usage / The Black Stone and its use" (in French). Retrieved 2007-03-06.
- Shuker, Karl P N (2007). Extraordinary Animals Revisited. CFZ Press.
- Rural Extension with Africa's Poor. "Black Stone" (PDF). Retrieved 2007-03-07.
- JKA Madaki. "Abstract: Clinical Presentation And Outcome Of Snake-Bite Patients At Zamko Comprehensive Health Centre, Langtang, Plateau State". Retrieved 2007-03-08.
- Chippaux JP, Ramos-Cerrillo B, Stock RP (April 2007). "Study of the efficacy of the black stone on envenomation by snake bite in the murine model". Toxicon. 49 (5): 717–20. PMID 17174999. doi:10.1016/j.toxicon.2006.11.002.