Botulinum toxin is a protein produced by the bacterium Clostridium botulinum, and is known to be highly neurotoxic. When introduced intravenously in monkeys, type A of the toxin exhibits an LD₅₀ of 40-56 ng, type C1 around 32 ng, type D 3200 ng, and type E 88 ng, rendering the above types some of the most powerful neurotoxins known. Popularly known by one of its trade names, Botox, botulinum toxin is now commonly used for various cosmetic and medical procedures.

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