Botulinum toxin

Botulinum toxin, botulinum neurotoxin, or botox is a neurotoxicprotein produced by the bacteriumClostridium botulinum and related species, and it is considered the deadliest known natural substance ever recorded in chemical literature. It prevents the release of the neurotransmitteracetylcholine from axon endings at the neuromuscular junction, thus causing flaccid paralysis. The toxin causes the disease botulism. Botulinum toxin is an acetylcholine release inhibitor and a neuromuscular blocking agent. Botulinum toxin was developed as a biological agent by the Soviet, United States, and Iraqi biological weapons programs. In strongly diluted form, the toxin is also used for medical and cosmetic purposes.

The seven main types of botulinum toxin are named types A to G (A, B, C1, C2, D, E, F and G). New types are occasionally found. Types A and B are capable of causing disease in humans, and are also used commercially and medically. Types C–G are less common.

In 2025, the structure of the complete 14 subunit botulinum neurotoxin complex (L-PTC) was solved.

Intoxication can occur naturally as a result of either wound or intestinal infection or by ingesting formed toxin in food. The estimated human median lethal dose of type A toxin is 1.3–2.1ng/kg intravenously or intramuscularly, 10–13ng/kg when inhaled, or 1μg/kg when taken by mouth.