How many units of botulinum toxin, and how is the dose calculated?

What is a unit and what does it measure?

A unit is the measure that describes the biological activity of botulinum toxin. It measures potency, not weight or volume.

Units of different botulinum toxin products are not directly equivalent. A dose of 20 units of one product corresponds to a different number in another, so comparing units only makes sense within the same product — which is why you should ask which one is being used, and be told.

The number of units and the volume injected are different things. The same number of units can be delivered in different volumes depending on dilution; volume affects spread, while dose is set by units.

What are the typical unit ranges by area?

The ranges below are the figures typically discussed. The dose given to you is set within that range once muscle strength has been assessed at examination.

• Forehead (frontalis) — 8–20 units
• Frown lines, glabella — 10–25 units
• Crow’s feet, one side — 6–12 units
• Masseter (jaw muscle), one side — 20–30 units
• Gummy smile — 4–8 units
• Underarm sweating, one side — 50 units
• Brow lift (lateral) — 2–4 units per side

Why is the dose not the same for everyone?

The dose follows the strength of the muscle. In the same area, the units given to a strong, thick muscle are markedly higher than those given to a weak one.

Expression muscles tend to be thicker and stronger in men, so the dose in the forehead and glabella is planned higher than in women.

The third factor is habit. In someone who frowns or raises their forehead all day, the muscle thickens and more units are needed for the same effect.

How is the dose decided at examination?

The dose is set by assessing the muscle in motion. You are asked in turn to raise your eyebrows, frown, close your eyes tightly and smile.

For the masseter you are asked to clench and the muscle is palpated. Its thickness and borders are established that way, and the dose positioned within the 20–30 unit range accordingly.

Brow height and eyelid level are also measured in the assessment. In a patient whose brow already sits low, a high dose to the forehead muscle would pull it lower still, so the forehead dose is capped against that measurement.

Does more units mean a better result?

No. Beyond a certain threshold, additional units stop movement entirely rather than improving the effect, and produce a frozen look.

Too much dose in the forehead brings the eyebrows down and makes the eyelid look heavy. The aim is not to end movement but to reduce the movement that creates the line.

A higher dose also does not extend the duration as much as expected; it usually stays in the 4–6 month range. What an unnecessarily high dose does raise is the risk of developing resistance over repeated treatments.

How many units in total in one session?

In cosmetic treatment the total across the upper face areas typically stays between 20 and 60 units. Adding masseter or sweating treatment raises the total.

The total dose in one session is capped by the doctor according to the indication and your general health. Where several areas are planned together, that cap is shared between them.

At least 3 months are left between repeat treatments. More frequent repetition raises the chance of developing resistance to the toxin and can make the same dose ineffective later.

Does the dose change on repeat treatments?

It can. With regular treatment the target muscle weakens over time, so the same effect can be achieved with fewer units and the interval between sessions can lengthen.

The first treatment usually lasts less time. By the second and third sessions the 4–6 month interval becomes more stable.

The dose is recalculated at every session; the same number is not repeated from the previous record. The note taken at the day-14 review is the main data that sets the next session’s dose — so if you were treated elsewhere, bring that record.