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Purpose and duration

Botulinum neurotoxin is used to reduce activity in overactive facial muscles. It is a symptom-control treatment rather than an operation on a blood vessel near the facial nerve. Benefit wears off, so treatment is commonly repeated. The Movement Disorder Society describes an average improvement lasting about three months, sometimes longer. An average is not a fixed appointment schedule or a promise about an individual's response.1

Assessing benefit across the whole cycle is useful: how much the spasms change, whether daily tasks improve, and how long unwanted effects or returning symptoms last. These are different questions from whether an injection was technically administered.

What Cochrane did and did not find

The 2020 Cochrane review searched for double-blind, parallel randomized comparisons of toxin type A with placebo in adults with HFS. It found no eligible trials and could not draw a trial-based conclusion for that question. Its authors also described an association between toxin treatment and improvement in observational data. The absence of eligible trials is not evidence that the treatment has no effect.2

Newer evidence asks additional questions

The 2024 systematic review includes 33 single-arm studies and two randomized comparisons. In those comparisons, participants in both groups received toxin around the eye; the randomized difference was added toxin versus placebo around the mouth. Such a design can examine an added component of treatment without testing the whole regimen against placebo. Most included studies were retrospective and uncontrolled, which limits causal conclusions.3

A 2025 randomized study compared two active toxin formulations in 87 patients over 12 weeks. This adds comparative evidence but does not establish lifetime outcomes, product interchangeability or superiority to surgery.4

Adverse effects and repeat treatment

The 2024 review reports eyelid drooping (ptosis), facial weakness, double vision and asymmetry among unwanted effects. It generally describes them as mild and transient in the included reports. That description cannot guarantee that every event will resolve in the same way or that risks are absent.3

Tell the treating clinician about both the useful effects and the unwanted changes across cycles. The reviewed evidence doesn't support claims that repeated injections routinely cause permanent facial paralysis, and the improvement seen in observational studies isn't a cure.

Discussing the treatment

Ask how success will be measured, what changes should prompt contact, and when the response will be reassessed. The clinician chooses the formulation and treatment approach for the person.

References

  1. International Parkinson and Movement Disorder Society. Hemifacial Spasm: Essential Facts for Patients. Webpage updated 2025; English handout ©2024. Source ↩
  2. Duarte GS et al. Cochrane Database Syst Rev. 2020;11:CD004899. doi:10.1002/14651858.CD004899.pub3. Source ↩
  3. Wang B, Wei X, Qi H, Bao X, Hu M, Ma J. BMC Neurol. 2024;24:420. doi:10.1186/s12883-024-03883-x. Source ↩
  4. A 12-Week Prospective, Double-Blind, Multicenter, Randomized Study Comparing 100 Units of Abobotulinum Toxin Type A (Dysport) and 33.33 Units of Neubotulinum Toxin Type A (Neuronox) for the Treatment of Hemifacial Spasm. Toxins. 2025;17(4):173. doi:10.3390/toxins17040173. PMID:40278671. PubMed ↩