Recently, there have been concerns about retrograde botulinum toxin transmission, meaning that the toxin could travel back to the central nervous system, causing long-term damage. Studies done in Italy by Flavia Antonucci have been mainly on a raw form of the toxin and not any of the commercially available preparations. Additionally, these studies have been performed on animals and with the injection of the toxin to one area and in a concentration of nearly 150 times greater than normal injections for cosmetic indications, which are spread over multiple sites.
Spread of toxin effects. The effect of botulinum toxin may affect areas away from the injection site and cause serious symptoms including: loss of strength and all-over muscle weakness, double vision, blurred vision and drooping eyelids, hoarseness or change or loss of voice, trouble saying words clearly, loss of bladder control, trouble breathing, and trouble swallowing.