Ricin is obtained from the beans of the castor oil plant (Ricinus communis), which is cultivated to extract the oil – the ricin remains in the solid fibre. It is a glycoprotein that interferes with protein synthesis in the cell, causing cell death. It has an LD50 of 1-20 milligrams per kg if orally ingested, but far less is required to kill if inhaled or injected

VX, resembling engine oil in consistency, originated from ICI's research on novel insecticides during the early 1950s. However, its extreme toxicity precluded its agricultural use. VX is lethal by disrupting the transmission of nerve signals between cells, which relies on the presence of acetylcholine. Once acetylcholine has transmitted its signal, it must be broken down to prevent continuous signaling by an enzyme catalyst known as acetylcholinesterase. Nerve agents like VX inhibit this enzyme, resulting in uncontrolled muscle contractions and ultimately leading to death due to asphyxiation.

Batrachotoxin causes death by disrupting sodium ion channels within muscle and nerve cells, effectively locking them in an open position, preventing closure. This uncontrolled migration of Na+ ions eventually leads to heart failure.

Maitotoxin is the most lethal of these substances, reckoned to have a LD50 about an order of magnitude less than batrachotoxin. Formed by a dinoflagellate, a kind of marine plankton, it has a very complicated structure, which presents a massive challenge to synthetic chemists. Maitotoxin is a cardiotoxin, it exerts its effects by increasing the flow of calcium ions through the cardiac muscle membrane, causing heart failure.

Scientists hold varying opinions regarding the comparative toxicities of different substances. However, there appears to be a consensus that botulinum toxin, produced by anaerobic bacteria, ranks as the most potent toxin ever identified. Its LD50 is exceptionally minute, with as little as 1 nanogram per kilogram being capable of fatally affecting a human. Extrapolating from its impact on mice, an intravenous dose as small as 10-7g would prove lethal to a person weighing 70 kilograms.