The results from Juvederm or other HA (Hyaluronic Acid) filler should be apparent immediately after injection, and generally should persist for 3-6 months after the injection.
It is not unusual to have some "extra" swelling immediately after the filler injection, which often makes the injection itself appear to have been "over-done". This extra swelling from the needle sticks usually dissipates within the first day or two, and can often be lessened by applying cold compresses to the injected areas.
If the HA filler material was injected "too deep" below the dermis, then it is possible that the initial "correction" of the lines and wrinkles quickly faded because it was mostly due to the needle sticks. In this case, the filler is too deep below the lines and folds to produce a demonstrable long-lasting improvement, even though technically the HA filler is still "there".
Lines that are caused primarily by over-active muscles, such as horizontal forehead creases and some peri-orbital lines, may require a combination of Botox to diminish the muscle activity, and HA filler to plump up the deep lines and wrinkles. The HA filler alone will not correct these "activity" frown and squinting lines.
Finally, one other possibility is that the lines and wrinkles are too deep for Juvederm or any other HA filler to do any good in the first place. In this situation, injecting a filler is like painting a portrait without stretching the canvas first. Such patients benefit more from a face lift, or perhaps a deep resurfacing procedure like CO2 laser or phenol peel, rather than wasting money on HA fillers which are inadequate to treat the real problem.