How does Plan B one step fail to work if you take it soon?

Plan B One-Step may fail to work if the individual is already pregnant at the time of taking it, as it is not effective in terminating an existing pregnancy. Additionally, its effectiveness can be influenced by factors such as body weight; it may be less effective in individuals with a higher body mass index (BMI). Other factors, such as incorrect timing in relation to the ovulation cycle or improper usage, can also contribute to its failure.