I was told its dangerous to put Botox into the shoulder muscles. While they have recommended doses, its still hard to tell how your muscles will react to the botox. If they inject too much botox - then your shoulder can 'collapse' onto your brachial plexus and cause more compression and problems....

I was also advised never to inject both sides at the same time -- for safety reasons. The botox can potentially spread to accessory breathing muscles or swallowing muscles. If you only do one side at a time -- you are sure to have the other side working properly.