A toxin made by the bacterium Clostridium botulinum. It can cause food poisoning. The drug Botox is a form of the toxin that can be used in small amounts to treat certain medical conditions. These include severe underarm sweating and severe muscle spasms in the neck and shoulders. Botulinum toxin A is also used to smooth wrinkles on the face. It is being studied in the treatment of pain in patients with skin leiomyomas (benign smooth muscle tumors) and other conditions. Also called Botox and botulinum toxin type A.