What is the typical onset and duration of BoNT-A effects?

• A. Onset 3–7 days; peak around 2 weeks; duration 3–6 months
• B. Onset 24 hours; duration 1 week
• C. Onset 2–4 weeks; duration 12 months
• D. Onset immediately; duration 2 weeks

Answer: (A)

BoNT-A works by blocking acetylcholine release at the neuromuscular junction, so its effect builds gradually as the toxin takes full effect on the injected terminals. You typically see onset in 3–7 days, with the strongest effect around two weeks, and the result lasting about 3–6 months as nerve terminals recover and new synaptic connections form. This time course is characteristic across common therapeutic and cosmetic uses of BoNT-A.

Patterns like a 24-hour onset with only 1 week of effect are too fast and short for standard BoNT-A action, a 2–4 week onset with a 12-month duration is too long, and immediate onset with a 2-week duration doesn’t match the usual progression of toxin effect and recovery.