Botulinum Toxin is a potent neuromuscular paralyzing agent that exerts its effect at the neuromuscular junction by entering nerve terminals and preventing the release of the neurotransmitter acetylcholine. It is injected directly into muscles, inducing localized weakness in the offending overactive muscles thereby reducing the force of unwanted contraction. Side effects are few and primarily involve greater than desired weakness in injected muscles or weakness in nearby muscles due to diffusion. Effects last approximately three months with strength and spasms returning as new nerve terminals are generated.