Botox is a brand name for botulinum toxin – a neurotoxin which blocks the messages sent by nerves to the bladder muscles.
When botulinum toxin is used to treat an overactive bladder these signals are blocked and the muscles relax, which reduces the frequency of the muscles contracting which causes an overactive bladder.
Botulinum toxin also relieves symptoms such as an urgent need to urinate and leaking urine.