Cyanide prevents cellular respiration leading to cell mortality. According to the Organisation for the Prohibition of Chemical Weapons, hydrogen cyanide inhibits metal containing enzymes necessary for cellular respiration. Cytochrome c oxidase, one of the enzymes affected by cyanide, contains iron and is responsible for the process that provides cells with energy through the use of oxygen.
Cyanide is a metabolic poison. It ultimately affects every cell in the body, but due to a higher demand for oxygen, it affects the central nervous system and cardiovascular system most rapidly. According to the National Institutes of Health, "Exposure to metabolic poisons can quickly cause seizures, respiratory failure, cardiac arrest, and death." The poison acts quickly at these levels. Lower levels cause less serious effects, but the individual still needs medical intervention.
The Centers for Disease Control and Prevention reports that exposure to small amounts of cyanide causes headaches, dizziness, nausea and vomiting, along with other symptoms. Exposure occurs by breathing cyanide gas, absorption through the skin and ingestion. Individuals suffering from cyanide poisoning should remove clothing, cutting any item that must otherwise come over the head and washing with large amounts of soap and water as quickly as possible. Avoid touching any areas on clothing with cyanide contamination.