The truth is, for Botox to become lethal, at least 3,000 units need to be delivered in a relatively short amount of time.
Most cosmetic Botox treatments use 100 units or less. That's a pretty sizeable safety margin.

Once you use Botox, you can't stop using it because your looks will change forever?
This is another common myth, but this one is based on nothing in reality. Botox changes your appearance slightly when it's active, which can be for 4 to 6 months. That amount of time is enough for many to get used to the “new you” and when it fades, they notice. So most who use Botox use it regularly (2-3 times a year). Since the cost for treatments is roughly equivalent to a trip to the spa, it's within reach of nearly everyone. In fact, the most common users are working mothers between ages 40 and 55 with a household income of $100,000 or less.

How do different doctors charge different prices for the same Botox?
 Botox varies by provider and by the particular area. Typically, the different areas that are treated include the lines in-between the brows (glabella), the forehead, and the “crow’s feet.” According to the American Society for Aesthetic Plastic Surgery (ASAPS), the cost per treatment in the United States averages between $300 and $500. Always ensure that your injector is experienced and properly trained; that you are getting FDA approved Botox Cosmetic from Allergan; and know how many units you receive. Pricing may also be lower if physicians use an assistant (that is often not a doctor) to provide injections. You should decide for yourself if you are comfortable with this before going to the office.

As Botox wears off it spreads in your blood stream and can affect other parts of your body?
This is an extension of the above myth. Because of the way that Botox works, it cannot spread beyond the area of the injection site. This is because of the way that it interacts with muscle tissue. Botox binds with chemical factories in nerve cells, preventing them from sending specific types of signals. Those signals are what tell muscles to contract, which is what causes wrinkling. When the muscles remain totally relaxed, wrinkles disappear. What Botox is doing is preventing the weakening muscles from contracting. The bind that Botox makes is in specific cells, so it does not spread once bound. As the clinical effect wears off, it’s not because Botox has broken free in its binding site, it’s because our body makes more receptors for those contractile signals

Botox is a scam because some doctors charge very little for the service and others charge exorbitant amounts?
This final point is about economics and marketing, not really about Botox. Like it or not, cosmetic surgery is almost always a free choice on the part of the patient and the physician. So the costs will be whatever the patient is willing to pay and the doctor is willing to accept. Yes, some physicians may charge large sums of money for Botox treatments, but those doctors are usually targeting a specific clientele who is willing to pay that price for whatever reason. Similarly, some doctors offer first treatments at extremely low cost – often lower than their own costs. This is to entice patients into their clinic to give Botox a try.
In both cases, the doctors are operating from the same background in regards to Botox. It all comes from the same supplier, Allergan; it all arrives refrigerated in little bottles; it all requires mixing to the specifications the doctor has for each treatment; and it all costs roughly the same no matter the doctor. The bottles are typically 2-dose bottles, meaning there is enough in there for two patients. So doctors will usually measure them out for a single treatment at half a bottle and then use the other half on a new patient, obviously avoiding any mixing in the process. Once the bottle is opened, it must be used within four hours, so doctors tend to schedule patients in pairs, back to back.

Written by Dr. Scott Blyer, New York City surgeon, Diplomate of the American Board of Cosmetic Surgery and CEO of Cameo Surgery