Almost everything an aesthetic injector does with botulinum toxin sits outside the approved label. Off-label neurotoxin dosing is therefore not an edge case or an advanced technique — it is the ordinary condition of the work, and the profession has responded to it badly, by circulating unit numbers as though they were established figures. Dr. Chris Croley teaches the alternative: a reasoning method that produces a defensible starting dose for a muscle nobody has published a dose for.
"With a lot of our neurotoxins we're treating in an off-label manner," he says. "And so there's no standardised dose for that muscle that's an FDA-approved label indication. But we can extrapolate."
The method below is the durable content. The numbers you produce with it are specific to one muscle in one patient on one day. That is the correct relationship between the two.
Why a reference table cannot solve this
The cosmetic on-label set is small — a handful of upper-face indications, and which ones apply depends on the specific product you are holding. That set also moves; approvals are added over time. Verify the current labelling for the product you actually use rather than working from memory.
Everything else you treat is extrapolated. Every widely circulated "units by muscle" chart for those regions is expert opinion, consensus statement or accumulated custom. Some of it is very good. None of it is label, and none of it accounts for the patient in your chair.
There is a second, harder reason a table cannot do this job. The right dose depends on the mass and strength of a specific muscle in a specific person, and those vary enormously between patients. A table has a single cell where the anatomy has a wide distribution.
Dr. Croley's warning about the consequence is one of the most important sentences in his teaching, and it should be preserved exactly as he framed it: "As we start treating other muscles all over the face and body, we actually start extrapolating that information, extrapolating those doses. And when we do that, we may have an unexpected response, because this has not been studied in large groups of patients."
That is not a disclaimer bolted onto the end. It is the epistemic status of the entire enterprise, and an injector who does not hold it in mind will eventually be surprised.
The inference method
Extrapolation is a comparison, and a comparison needs an anchor. Dr. Croley names the anchors he uses: "We can say, what is our normal dose in a masseter? What is our normal dose in the glabellar complex, or the frontalis? And then we can make an assessment: is this muscle a similar size? Is it a bigger muscle? Is activity more? And I'm going to adjust my dose up or down."
Four variables drive the inference, and two further variables govern how far you then back off.
1. Size
Muscle mass, not skin surface area. This is the most common error in extrapolation: injectors scale by the area of the treatment zone rather than the volume of muscle underneath it. A broad thin sheet and a compact thick bundle covering the same footprint need very different doses.
Think in terms of cross-section and bulk. How much contractile tissue is actually there?
2. Density
Two muscles of the same dimensions can differ markedly in how much force they generate and how much toxin it takes to quiet them. Dr. Croley points straight at the clinical signal: "If this is a young guy with a really thick, dense muscle, we're probably going to have to use a higher number of units or a higher dose."
Sex, age, habitual loading and hypertrophy from repeated use all shift density. A bruxer's masseter and a non-bruxer's masseter are not the same organ, which is why the same nominal dose produces different results — a point that runs through the practical literature on bruxism management and jaw clenching.
3. Activity
How hard does this muscle actually work in this person? Palpate it under contraction. Watch it during animation. Dr. Croley's assessment step is explicit — "we need to assess the muscle, we need to assess the muscle strength" — and it is an examination, not an inference from the patient's photograph.
Activity and size are independent. A small, ferociously active muscle may need more than a large, lazy one.
4. The anchor
Choose the labelled or well-characterised muscle you dose most routinely that is most similar in size, density and activity to your target. The quality of your extrapolation is limited by the quality of your anchor, so choose one you genuinely have consistent personal experience with — your frontalis dosing, your glabellar complex dose, your masseter dose.
Then reason in ratios rather than absolutes. If the target muscle is roughly half the mass of your anchor with comparable density and activity, your unadjusted starting point is roughly half your anchor dose. If it is half the mass but noticeably denser, adjust upward from there. The arithmetic is crude on purpose. It is a starting point, not a calculation.
5. Role — the first discount
Dr. Croley's placement instruction includes two variables beyond the muscle itself: place the dose "according to muscle size, strength, the role of the muscle, and the risk."
Role asks what this muscle does for the patient's face and how much they value it. An elevator that produces the patient's smile is a high-value muscle; overshooting it costs the patient something she notices every time she looks in a mirror. A depressor contributing to a downturned commissure is lower-value; the patient is asking you to reduce it.
High-value muscles get a larger discount off your extrapolated figure.
6. Risk — the second discount
Risk asks what sits adjacent to and beneath the target, and what happens if some of your dose reaches it. A muscle surrounded by low-consequence neighbours tolerates a more confident dose. A muscle sitting directly on top of one whose weakness would be disfiguring — the depressor anguli oris over the depressor labii inferioris being the definitive example — demands the largest discount of all.
Risk is an anatomical judgement, which is why the method collapses without anatomy. Dr. Croley opens his teaching on this subject by saying so: "If you have a weak understanding of anatomy, it's going to be really difficult for you to come up with complication management strategies."
The method as a sequence
Run it in this order. The order is load-bearing, because the discounts must come last.
- Name the muscle precisely — and be able to state its borders, its depth, its plane, and what is immediately beside it and beneath it.
- Examine it. Palpate at rest and under contraction. Assess bulk and strength in this patient, not in general.
- Choose the anchor from muscles you dose routinely and consistently.
- Scale for size, reasoning in ratios of mass.
- Adjust for density and activity, up or down.
- Apply the role discount — how much does the patient value this movement?
- Apply the risk discount — how bad is spillover here?
- Decide distribution, not just total. A broad muscle takes a fractionated dose across several points; a small focal muscle takes one. In the correction case Dr. Croley teaches from, the mentalis was fractionated across the muscle rather than deposited in a single bolus.
- Go under the figure you arrived at. "I want you to always be conservative. You can always add more. It's hard to take this away."
- Reassess at two weeks and record the outcome.
Two worked reasonings
Notice that neither produces a number here. That is deliberate — the number belongs to the patient in front of you, and publishing one would invite exactly the copying this method exists to replace.
A zygomatic elevator in a thin patient. Small muscle, modest mass, and in a thin patient there is little tissue to absorb a deposit. Anchor it to the smallest muscle you dose routinely and scale down for mass. Then apply both discounts hard: the role is high-value, because this muscle produces the patient's smile, and the risk is high, because the consequence of overshoot is a visibly altered smile that the patient will not accept. The extrapolated figure should end up well below where the size comparison alone would put it.
A masseter in a young male bruxer. Large muscle, high mass, high density, high activity — three variables all pointing the same direction. Anchor to your own usual masseter dose and adjust upward for density and activity. The role discount is small, because the patient is asking you to reduce this muscle's action. The risk discount is real but geographically specific, driven by what sits at the anterior border. The net result is a figure above your typical masseter dose rather than below it, which is the correct output: the method should move you up as readily as down.
The liability position, stated honestly
Off-label use of an approved drug within a clinician's scope of practice is ordinary, lawful medical practice, not experimentation. That is the starting point, and it should not be apologised for.
What is true alongside it is that the evidence supporting an extrapolated dose in an unlabelled muscle is thinner than the evidence supporting an on-label one, and patients are entitled to know that. Dr. Croley's framing — "this has not been studied in large groups of patients" — is the plain-language version and it is a good one to say out loud.
Practically, three things follow:
- Consent should name the off-label status of the specific treatment, in terms the patient understands, rather than burying it in a generic form.
- Documentation should record the reasoning, not just the dose. "Extrapolated from masseter dose, adjusted up for density in a young male bruxer, started below calculated figure, review at two weeks" is a defensible note. A bare unit count is not.
- The uncertainty should shape the dose, not just the paperwork. If you genuinely do not know how a muscle will respond, the correct expression of that is a smaller first dose.
Build your own dataset
The highest-value output of this method is not any individual dose. It is the record.
Keep a log: muscle, patient characteristics, anchor used, the reasoning, the dose given, the effect at two weeks, and the observed duration. After twenty or thirty entries in a given muscle you are no longer extrapolating from someone else's anchor — you have your own, grounded in your own product, your own reconstitution, your own technique and your own patient population.
That is how an injector stops needing dose charts. Not by memorising better ones, but by generating data.
What not to do
- Do not transfer units between products. OnabotulinumtoxinA, Dysport, Xeomin, Jeuveau and Daxxify are not unit-interchangeable, and a dose reasoned out for one does not carry across to another. Re-anchor within the product you are using.
- Do not scale by surface area. Mass, not footprint.
- Do not copy a number from a chart, a lecture slide or a social media post without knowing what anchor produced it, in which product, at what dilution, in what patient population.
- Do not treat a confident number as a validated one. Confidence and evidence are unrelated variables in this domain.
- Do not extrapolate without the anatomy. If you cannot name what is beneath the muscle, you cannot apply the risk discount, and the risk discount is the one that prevents the serious complications.
These figures and this approach reflect Dr. Chris Croley's clinical practice as taught in Empire Medical Training's hands-on curriculum. Technique is learned under supervision; this article is educational and is not a substitute for training.
The method only works on top of real anatomical knowledge, which is why Empire teaches these regions on tissue as well as in theory. The foundations sit in Anatomical Based Aesthetics Training, and the applied dosing work in Advanced Botulinum Toxin & Filler Training. A general orientation to the regions involved is available in the facial mapping reference.
Related guides in this cluster
Part of Neurotoxin Reconstitution and Dosing.
Clinical GuideOn-Label Reconstitution Across the US Neurotoxins — A Reference Table for InjectorsA complete on-label neurotoxin reconstitution chart for Botox, Dysport, Xeomin, Jeuveau and Daxxify — vial sizes, diluent volumes and u
Clinical GuideWhy a Unit of Botox Is Not a Unit of DysportBotox units vs Dysport units are not the same measure. Units are defined by each manufacturer's own potency assay — here is why no conv
Clinical GuideBacteriostatic vs Preservative-Free Saline — What the Benzyl Alcohol Actually DoesBacteriostatic saline for neurotoxin reconstitution is off-label but well studied. What benzyl alcohol does to injection pain, potency
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Explore Botox Training & Certification →Disclaimer
This article reflects the clinical opinions and experience of Dr. Chris Croley, Chief Medical Officer, Empire Medical Training, an independent faculty member contributing to Empire Medical Training's curriculum. The views expressed are the author's own and do not necessarily represent those of Empire Medical Training.
It is professional education, not medical advice, and is no substitute for hands-on training or independent clinical judgment. Licensed clinicians remain responsible for their own patient selection, technique and outcomes, for verifying current product labelling, and for practising within their scope and applicable law. Empire Medical Training accepts no liability for reliance on this content.