protein toxin produced by the anaerobic bacterium Clostridium botulinum. There are seven serotypes (A, B, C, D, E, F, G), of which types A, B, E, F, and G are used in humans.

It inhibits the release of acetylcholine, a key neurotransmitter at the neuromuscular junction, leading to muscle paralysis.

When injected into muscle tissue, muscle relaxation and paralysis typically appear within about 3 days and last for approximately 3 to 8 months.