What it is
OnabotulinumtoxinA is the generic name of the botulinum toxin type A preparation sold in the United States as Botox and, for cosmetic indications, Botox Cosmetic. It is a protein made by the bacterium Clostridium botulinum, purified and supplied as a powder that a clinician dissolves in saline before injection.
Injected into a muscle, it blocks the chemical signal that tells that muscle to contract. The muscle relaxes for a few months, then recovers as nerve endings regrow their connections. The same principle is behind both the medical uses, such as neck dystonia or an overactive bladder, and the cosmetic ones, where relaxing a frown muscle softens the line above it.
The strength of the product is measured in Units. Those Units belong to this preparation only and do not convert to the Units of any other botulinum toxin product.
OnabotulinumtoxinA is a purified botulinum neurotoxin type A produced by fermentation of Clostridium botulinum type A (Hall strain) and supplied as a sterile vacuum-dried neurotoxin complex with human albumin and sodium chloride. The core neurotoxin is a 150 kDa dichain protein: a ~100 kDa heavy chain and a ~50 kDa light chain joined by a disulfide bond.
The heavy chain binds SV2 and polysialogangliosides on presynaptic cholinergic terminals and mediates endocytosis and translocation of the light chain into the cytosol. The light chain is a zinc-dependent endopeptidase that cleaves SNAP-25, a SNARE protein required for fusion of acetylcholine vesicles with the presynaptic membrane. Transmission is blocked until new terminals sprout and SNAP-25 is replenished, which is why clinical effect is temporary and the label sets minimum retreatment intervals.
Potency is assigned by a manufacturer-specific assay. The label states explicitly that Units of BOTOX are not interchangeable with those of other botulinum toxin products.
Who made it and when
The ophthalmologist Alan B. Scott began injecting purified botulinum toxin into eye muscles in the 1970s, looking for a non-surgical way to correct a squint. He called the product Oculinum, which translates roughly as “eye aligner”. The FDA licensed Oculinum in December 1989 for strabismus and for blepharospasm, the involuntary closing of the eyelids.
Allergan, which had distributed the product, acquired it in 1991 and renamed it Botox. Over the next three decades the approved list grew in two directions at once: neurological and urological uses under the Botox name, and facial line indications under Botox Cosmetic, starting with frown lines in 2002. Allergan is now part of AbbVie.
Scott’s work at the Smith-Kettlewell Eye Research Institute, published from 1980 onward, established intramuscular botulinum toxin type A as a reversible chemodenervation agent. Oculinum was licensed under BLA 103000 on 29 December 1989 for strabismus and blepharospasm associated with dystonia in patients 12 years and older. Allergan acquired Oculinum Inc. in 1991 and rebranded the product BOTOX.
Subsequent US approvals under the same BLA include cervical dystonia, severe primary axillary hyperhidrosis, upper and lower limb spasticity in adults and in paediatric patients, urinary incontinence due to detrusor overactivity associated with a neurologic condition, overactive bladder, paediatric neurogenic detrusor overactivity from 5 years of age, and prophylaxis of headaches in chronic migraine (15 October 2010). The cosmetic franchise adds glabellar lines (2002), lateral canthal lines (2013), forehead lines (2017) and platysma bands (October 2024).
What the data say
The evidence base is unusually large for an injectable of this kind, because each indication needed its own trials. In chronic migraine, two matched trials called PREEMPT 1 and PREEMPT 2 enrolled nearly 1,400 adults between them and injected a fixed pattern of 31 sites totalling at least 155 Units every 12 weeks. Pooled, they reported fewer headache days than placebo, and that result is the basis of the migraine approval.
The most recent approval, for the vertical neck bands called platysma bands, rests on two placebo-controlled trials of roughly 400 participants each, reported in 2024. Across indications the reported adverse events are mostly local, but the label carries a boxed warning because toxin effects can appear away from the injection site.
PREEMPT 1 (NCT00156910, n=679) and PREEMPT 2 (NCT00168428, n=705) used identical 24-week double-blind phases followed by a 32-week open-label phase, with a fixed-site fixed-dose paradigm of 155 to 195 Units per cycle. PREEMPT 1 missed its original primary endpoint of headache episodes but met headache-day endpoints; PREEMPT 2 met its primary endpoint of change in headache days, and the pooled analysis, which supported registration, reported a significant between-group difference in headache days at week 24 with a tolerability profile dominated by neck pain and muscular weakness.
The platysma programme comprised two multicentre placebo-controlled phase 3 studies, M21-309 (NCT04949399, n=408) and M21-310 (NCT04994535, n=426), with a co-primary of investigator- and participant-assessed improvement. Participants were randomised by baseline severity to a single treatment of 26, 31 or 36 Units, or placebo, with the primary assessment at day 14. Immunogenicity remains a recognised limitation across indications: neutralising antibody formation can reduce response with repeated high-dose exposure.
Regulatory picture
In the United States the FDA-approved products containing onabotulinumtoxinA are Botox and Botox Cosmetic, both from Allergan, an AbbVie company. Nothing else containing this molecule is approved here. Botulinum toxin products that hold only a foreign licence and are imported or sold online for injection are not FDA-approved.
The FDA has acted on that repeatedly. In April 2024 it alerted the public that counterfeit Botox had reached patients in several states, and the CDC reported harmful reactions in 19 people in nine states. In November 2025 the FDA announced 18 warning letters to websites marketing unapproved and misbranded botulinum toxin products. Compounding does not apply to a licensed biologic of this kind.
OnabotulinumtoxinA is licensed under BLA 103000. As a biological product it is not eligible for the 503A bulk drug substances route, and no legal pathway exists for a pharmacy to compound a copy, so the compounding field is recorded here as not applicable rather than restricted.
Unapproved botulinum toxin products entering the US market are unapproved new drugs under section 505 and misbranded under section 502 of the FD&C Act. FDA’s April 2024 alert described counterfeit material bearing an outer carton naming the active ingredient as “Botulinum Toxin Type A” instead of “OnabotulinumtoxinA” and strengths not produced by the manufacturer. The November 2025 action targeted 18 websites offering unapproved and misbranded botulinum toxin products in the United States. Clinical harm reported to CDC in 2024 was consistent with systemic botulinum toxin effect, and four patients received botulism antitoxin.
