What matters when you have your Botulinum toxin (Botox) is the overall number of units that you are given. Practitioners may choose to dilute their Botox with varying amounts of saline, and this will affect how far the Botox diffuses away from the injection site. Personally, when I am treating frown lines between the eyebrows in the frown line (Glabella) region I like to use it in quite a concentrated form (100 units of Botox diluted in 1 ml of saline, giving 10 units per 0.1ml), as I want the Botox diffusion to be quite limited. When I am treating horizontal forehead lines I prefer to use it in a more dilute form (100 units in 2mls of saline) so that I can achieve more diffusion of the botox over a wider area of muscle.
So why does the total number of units that you are given matter so much? Because studies have shown a clear dose-response relationship between the duration of effect and the dosage that you are given. If you are given 20 units of Botox into your glabella frown line region it will last about 16 weeks in 75% percent of clients, whereas if clients are given half that dose it will only last that long 35% of the time, and you will therefore probably be needing more treatment well before the end of four months after your last treatment with this dosage.
So if you are of average build and normal facial muscles mass, and you are having the frown line and your forehead treated with Botox you should probably be getting a total dosage of around 40-50 units. This will reliably achieve an effect that is going to last you for the next four months or so. Clearly if you are exceptionally lean or exceptionally well endowed with facial muscles then the dosage will need to be altered accordingly.
Don’t forget that if your if your doctor is using Dysport (marketed under the name of Azzalure in Europe) then the number of units will be different. It will be about 3 times higher than with Botox or Xeomin as Dysport/Azzalure, unit for unit, is only one third as powerful as Botox. So one unit of Botox is equivalent to around 3 units of Dysport / Azzalure. When given in appropriate dosage studies have shown that Dysport/Azzalure is as effective as Botox. So ask your practitioner about the total dosage they are planning to use. If it’s a lot less or a lot more than the quantities mentioned above for the forehead and frown line areas, ask them why.