Botox units vs Dysport units is a comparison that looks like a currency exchange problem and is not one. A unit is not a quantity of drug. It is not a mass, a volume, or a count of molecules. It is a measure of biological activity established by a specific manufacturer, using a specific assay, against that manufacturer's own reference standard — and the moment you change any of those three things, the number stops meaning what it meant.
Dr. Chris Croley, Chief Medical Officer at Empire Medical Training, puts the point bluntly in Empire's neurotoxin curriculum: "Keep in mind, those units are fairly arbitrary. The company decides how many units they're going to label that vial with. But when they're actually making this product, they weigh it, they deliver it by weight, and they do a study of how much toxin it takes to get a desired clinical result."
That is the whole construct. Product is manufactured and filled by mass. Potency is then characterised by assay, and the vial is labelled in units of that assay. Two manufacturers running different assays against different reference standards will land on different numbers for biologically comparable material — not because one is stronger in some universal sense, but because they are measuring with different rulers.
What a unit actually is, product by product
The prescribing information for each US botulinum toxin type A product describes its own potency unit, and the descriptions are worth reading side by side because the differences are not cosmetic.
BOTOX Cosmetic and BOTOX (onabotulinumtoxinA). The label states that the primary release procedure uses a cell-based potency assay to determine potency relative to a reference standard, that the assay is specific to AbbVie's products, and that one unit corresponds to the calculated median intraperitoneal lethal dose (LD50) in mice. It then adds the operative sentence: due to specific details of this assay such as the vehicle, dilution scheme and laboratory protocols, units of biological activity of BOTOX Cosmetic cannot be compared to nor converted into units of any other botulinum toxin products assessed with any other specific assay method.
DYSPORT (abobotulinumtoxinA). The label states that the primary release procedure uses a cell-based potency assay, that the assay and reference material are specific to DYSPORT, and that one unit corresponds to the calculated median lethal intraperitoneal dose in mice. Same construct, different assay system, different reference material.
XEOMIN (incobotulinumtoxinA). Cell-based potency assay, one unit corresponding to the median intraperitoneal lethal dose in mice, with the label noting that as the method for conducting the assay is specific to XEOMIN, its units cannot be converted into units of any other botulinum toxin assessed with other specific assays.
JEUVEAU (prabotulinumtoxinA-xvfs). The label describes an animal-based potency assay specific to Evolus' product, with one unit corresponding to the calculated median intraperitoneal lethal dose in mice.
DAXXIFY (daxibotulinumtoxinA-lanm). The label states that the potency units are specific to the preparation and test method used, and that they are not interchangeable with other preparations of botulinum toxin products.
Read those together and the pattern is unmistakable. Every manufacturer defines its unit against its own standard, several have moved from animal assays to cell-based assays over time, and every single label contains an explicit prohibition on conversion. This is not boilerplate legal caution. It is a statement about what the measurement is.
Why the LD50 heritage explains the divergence
The mouse LD50 assay is the historical root of the botulinum potency unit: one unit is the dose that kills half of a population of injected mice. That definition sounds absolute until you consider what varies between laboratories running it.
The strain, sex, age and weight of the mice vary. The vehicle the toxin is diluted in varies — and because botulinum toxin adsorbs to surfaces and is sensitive to dilution conditions, the vehicle materially affects recovered activity. The dilution scheme varies. The injection protocol and observation period vary. Each of those introduces a systematic offset, and the offsets do not cancel.
The result is that two manufacturers can assay biologically similar preparations and arrive at unit counts that differ substantially, purely as a function of how they run the test. The unit is internally consistent — a manufacturer's own units are reliably comparable to its own units, batch to batch, which is precisely what a release assay is for — and externally meaningless.
Several manufacturers have since replaced the mouse LD50 as the primary release assay with cell-based potency assays, which are more reproducible and remove the animal burden. That change did not create a common scale. Each cell-based assay is still calibrated to its own manufacturer's reference standard, which itself traces back to that manufacturer's historical unit. The rulers were re-engineered; they were not standardised against each other.
Why published ratios are not conversions
Injectors encounter numerical relationships between products constantly — in comparative trials, in review articles, in manufacturer education, in conversation. It is worth being precise about what those numbers are and are not.
Comparative clinical studies do exist, and they generate dose relationships for the specific conditions they studied: a particular indication, a particular muscle group, a particular patient population, a particular pair of reconstitution concentrations, a particular endpoint measured at a particular time point. Those relationships describe what happened in that study. They are not exchange rates.
Three reasons the distinction holds at the chairside.
The relationship is not stable across indications. A dose relationship derived from glabellar treatment does not transfer to masseter, axillary hyperhidrosis or cervical dystonia, because the target tissue, injection depth, receptor density and endpoint all differ.
The relationship is not stable across endpoints. Onset, peak effect, field of effect and duration are separate outcomes, and two products matched on one are not necessarily matched on the others. DAXXIFY is the clearest current example: it is approved at a 40 Unit glabellar dose delivered in five 8 Unit aliquots, and its clinical positioning rests on duration rather than on peak effect, which makes a single-number equivalence to any other product incoherent before you even start.
Reconstitution is a confounder. Field of effect varies with injected volume, as Hsu, Dover and Arndt demonstrated in Archives of Dermatology in 2004 when equivalent unit doses delivered in a fivefold larger volume produced roughly 50% greater affected area. Any cross-product comparison that does not hold concentration constant is comparing two things at once.
Empire does not publish an inter-product conversion factor, and Dr. Croley does not teach one. The instruction he gives is the one the labels give: dose each product according to its own labelling and the evidence for the indication you are treating.
What this changes at the chairside
The practical consequence is a set of habits rather than a formula.
Learn each product's dosing natively. If you treat glabellar complex with BOTOX Cosmetic at 20 Units total in five 4 Unit aliquots, and you add DYSPORT to your practice, the number you need is DYSPORT's own: 50 Units total in five 10 Unit aliquots. You do not derive it. You learn it. DAXXIFY's is 40 Units in five 8 Unit aliquots. These are three separate facts, not one fact expressed three ways.
Never carry a volume habit across a product. This is where unit non-equivalence becomes a real dosing error rather than an abstraction. An injector running BOTOX Cosmetic at 4 Units per 0.1 mL who has internalised "one tenth per point" and then picks up a DYSPORT vial reconstituted to 20 Units per 0.1 mL delivers 20 Units where the label instructs 10. The unit construct and the volume construct fail together.
Document the product by name, the dose in units, and the concentration. "20 units toxin, glabellar" is not an adequate record. When the patient returns, or presents to another clinician, the product name is what makes the unit figure interpretable. Empire's material on what to include in Botox consent forms covers the documentation side in more depth.
Handle the patient conversation honestly. Patients compare unit counts between practices and between products, and a higher unit number reads as a higher dose. Croley notes how the naming problem starts: patients "use that name [Botox] synonymously with neurotoxin, and then we guide them to whichever toxin we want them to be treated with in our practice." The explanation that lands is the ruler analogy — different manufacturers count in different units, the way distance is the same whether you state it in miles or kilometres, and the number on its own tells you nothing without knowing which scale it is on.
Do not switch products mid-plan without re-deriving the plan. If a patient's usual product is unavailable and you substitute, you are not adjusting a dose. You are writing a new one, from that product's own labelling, and the treatment interval, expected onset and expected duration may all shift with it.
Dr. Croley's teaching points here reflect his 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 one thing units do tell you
None of this makes units useless. Within a single product, the unit is a rigorously controlled, batch-to-batch reproducible measure of biological activity, and that is exactly what it needs to be. It lets you reproduce a result in the same patient across visits, titrate deliberately, compare your own outcomes over time, and communicate unambiguously with a colleague who is using the same product.
The unit is a precise internal measure and a meaningless external one. Treating it as the first and never the second is the whole discipline.
Injectors working across more than one neurotoxin can develop that discipline with live product and supervision in Empire's Cosmetic Neurotoxins Training and Complete Botox Training workshops; those building broader combination treatment plans may also want Advanced Botulinum Toxin and Filler Training.
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 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
Clinical GuideConcentration as a Clinical Instrument — How Dilution Governs DiffusionNeurotoxin dilution and diffusion, worked as a decision. When to choose a tighter concentration, when to choose a looser field, and wha
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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.