Side effects are rare; indeed it is one of the safest cosmetic procedures available. Occasionally a temporary drooping of the eyelids or eyebrows may occur, but this only last a few weeks. Rarely a transient numbness develops in the treated area. As with any injection there is a small risk of infection. Minor bruising may occur at the injection sites, and if you are prone to cold sores, treatment may bring out an eruption. Finally an extremely rare side effect is weakness and fatigue. In one study less than 3% of patients experienced any of these complications.