Botox (onabotulinumtoxinA) was approved for the treatment of wrinkles between the eyebrows in 2002, while Dysport (abobotulinumtoxinA) was approved for the same therapy in 2009. They are both botulinum toxin compounds - a protein produced by the bacterium Clostridium botulinum.
Botulinum toxin is a neuromodulator - it affects nerve impulses. It is useful in cosmetic medicine because it prevents wrinkle formation by paralyzing facial muscles.

In this study, the scientists applied Botox to one side of the face and Dysport to the other side of the same face of 90 volunteer patients. They were being treated for crow's feet - wrinkles in the outer corner of the eyes that develop as we get older. Crow's feet is medically known as "lateral orbital rhytids".
Each patient's appearance was assessed by the scientists using a 5-point scale. They also gathered data on patient feedback.
When patients were asked to squeeze (contract) their facial muscles as much as possible, Dysport scored considerably higher than Botox. 67% of the participants said they clearly preferred the Dysport results, compared to 33% who favored Botox.
Neither the scientists nor the participants could differentiate between the two when the patients' faces muscle were relaxed.
The authors concluded: "AbobotulinumtoxinA offers superior efficacy in the treatment of lateral orbital rhytids compared with onabotulinumtoxinA. Further studies are needed to compare the 2 products in different muscle groups and for other indications." 

Both Medicis Aesthetics Inc. (makes of Dysport) and Allergan Inc. (makes of Botox) were approached for funding for this study. Only Medicis Aesthetics responded with money.

Source: Medical News Today