When injected into a muscle it causes weakness or paresis of that muscle. The skin overlying the muscle becomes softened and relaxed.
In most people the effect lasts 3-4 months, so about three procedures are necessary a year to see consistent results. After the first year of keeping up with the injections the effects can actually last longer; Some individuals can see results last for 5-6 months and only need 2 procedures a year.
The effect of Botulinum A Toxin begins to appear in 2-6 days, peaks in 1-4 weeks and gradually declines after 3-4 months.