Botox should only be injected by trained medical professionals

Botox should only be injected by trained medical professionals (Plastic Surgeons, Dermatologists). 

In California, RN's may inject Botox if properly trained and only under the supervision of a physician. 

Occasionally (underline occasionally as this is uncommon) a bit of the Botox can get into the muscle of the upper eyelid and cause it to droop.  Fortunately, this is usually short lived as the muscle was not injected directly.  Over-injection can cause facial immobility. 

In the right hands, Botox is very safe and the vast majority of patients who are properly injected by trained professionals are very happy with results. 

Do your homework first and beware of highly discounted prices.