Botox achieves its optimum results within 7 to 10 days and lasts and average of 4 to 6 months. The effect of Botox gradually reduces after 3 months and muscle strength slowly returns. When the line / wrinkle starts to reappear, a simple repeat treatment is all that is necessary to maintain the desired result. After several injections, the effects last longer and treatments may only need to be performed again once every 6 months.