The first place to start when lines that fold with expression are the concern.
Wrinkles form when the same expression folds the skin over and over. Putting medication into the muscle behind that expression reduces its pull, so the skin stops folding and the line softens. It suits lines that appear with expression more than creases already set in. The effect builds over about 2 weeks and lasts 3–4 months.
One session lasts three to four months. It takes about two weeks to take effect, and during that time the habit of folding the skin in that expression loosens. With repeat sessions the line settles in more slowly, so the interval often stretches a little each time.