Botulinum toxin products have an amazing safety record. Yet every drug has side effects including these products. Generally we distinguish two levels of treatment: doses associated with cosmetic uses and doses associated with medical use. While it is possible but not common to have mild systemic effects with cosmetic doses, much more serious side effects are associated with the dosages used for medical indications. It is these types of side effects that prompted the FDA to require what is called a black box warning for these products. Interesting while the FDA now requires this warning, they also make clear that the most serious side effects have not been associated with the dosages used for cosmetic purposes. If you are going to have a side effect, they usually begin to make their presence known within a few days of when the treatment was performed. An example of this is upper eyelid ptosis after a BOTOX treatment. Because these products take a few days to work, these types of symptoms and signs often initially present as something bothersome that becomes more bothersome over a several day period. Hopefully your question is theoretical and you are not experiencing this type of issue. If you are, it is important to communicate with your injecting physician and be immediately assessed for the problem.
Typically side effects of Botox such as a droopy eyebrow or eyelid develop within the first 10 days, and the duration of this is variable, and never longer than 4 months. If Botox is injected by a highly trained and experienced physician, the likelihood of any side effects is remote. ~ Dr. Benjamin Barankin, Toronto Dermatology Centre.