What are the health implications of using botulinum toxin frequently?

Botulinum toxin has been used for almost 30 years to treat spasticity. Out of these experiences it shows that botulinum does not cause long-term side effects. Microscopic examinations showed that no permanent changes have occurred in the nerves or muscles after absorbing Botulinum. After the effect ends, neither the active substance nor its effects on the nerves can be detected. As a calm muscle is usually weaker (think of a leg in a cast), with time a smaller dose of Botulinum toxin is going to be needed, to get the same muscle relaxing effect than before.