The thing people are not told
Neuromodulator does not switch a muscle off, it reduces how strongly it can contract, and it does that gradually as the drug binds. So the first week is a slope rather than a step, and it is a lumpy slope: the left side commonly moves before the right, one eyebrow can sit higher than the other for a few days, and the forehead often softens before the glabella does.
Almost every message we get in week one is about asymmetry at day five. It resolves in nearly every case, and adjusting it before day fourteen means treating a moving target and frequently overdoing it.
What it will not do
Remove a line that is already etched into the skin at rest. Neuromodulator stops the movement that deepens a line; it does not fill one that twenty years of movement has already carved. A deep static glabellar line will soften considerably over several treatments as the skin gets a chance to remodel, and it will not disappear at two weeks.
If a line is visible when your face is completely still and relaxed, that portion of it is a skin problem, and it belongs to microneedling, resurfacing or in some cases a small amount of filler. Anybody who tells you otherwise is selling you a second syringe in three months.
How long it lasts
Three to four months for most areas and four to six for masseter. It does not stop abruptly: movement returns gradually over several weeks, and most people book their next appointment when they notice it starting rather than on a calendar.
Treating before three months is not more effective and does raise the theoretical risk of developing antibodies, which is rare and is a real reason not to top up early.