Botulinum toxin injections are used to decrease spasticity. Spasticity is typically seen in strokes, multiple sclerosis, writer's cramp, cervical dystonia, traumatic brain injury, etc. It has also been approved for use in blepharospasm, hemifacial spasm, and hyperhidrosis.
I use Botox from the Allergan Company. It works by blocking the nerve signal to the muscle which causes the muscle to relax and not spasm. It does 'wear off' but typically lasts about three months. After this time, it can be reinjected if it was helpful.
Strokes can cause pain and reduced function. When spasticity develops it can cause pain from the muscle tightness itself or causes excess strain on joints from the muscles tighting up and twisting. If the fingers and hand are 'curled up' limiting function, Botox may be useful here as well.	Cervical dystonia is a tightening of the neck muscles which can cause the head to move into different positions. However, the head may remain straight in some cases.
Hemifacial spasm is uncontrollable contraction of the facial muscles typically on one side of the face. Blepharospasm is similar but only affects the eyelids.	Hyperhidrosis is excessive sweating at the axilla. It can be embarassing but is treatable with Botox.