How many units of Botox does it usually take to get rid of "smoker's" lines on the upper lip?

I have been treating smoker's lines (aka lipstick bleeding lines) for over two decades. Tiny droplets of Botox (usually about 3-4 units) are all that are required to soften muscular overactivity (not freeze) of the perioral muscle in large measure is involved in their formation and perpetuation. Over or inappropriate treatment can result in problems with drinking, eating, speaking and playing wind instruments. I have also found the addition of a small amounts of a filler, such as Belotero Balance (which has little to no tendency to give rise to the unwanted, bluish Tyndall Effect, when injected superficially into the tissue around the mouth). As a rule, combining Botox with filler leads to a more prolonged effect than that which may be achieved with either injectable alone. If required a series of superficial peels with high concentration glycolic acid or Jessner's solution may be useful for improving the overall tone and texture of the skin.The above techniques are advanced injection techniques that are best left to the hands of a board certified aesthetic physician with experience and expertise in treating this functionally important area. 

Thank you for your question.  The puckering of the upper lip that contributes to the vertical smokers lines can often be treated with small amounts of botox, normally in the 4-6 unit range for the entirety of the upper lip.  Any wrinkles that remain afterwards would best be treated with fillers to camouflage their appearance.  Hope that this helps.