Is three weeks long enough to be nicotine free before a breast reduction?

There is no absolute consensus as to the length of time a person should abstain from nicotine prior to a breast reduction. In general, the longer, the better and my personal feeling is that 3 weeks is inadequate. Many factors come into play that would affect timing. These include how much a person smokes in a day, how long they have been smoking, the size of the breasts before surgery, and general medical health. These factors would all be considered by your surgeon who therefore is the best person to make the recommendation regarding timing. 

Recommendations will vary from one practice to another;  therefore your plastic surgeon will have the most relevant recommendations for you. In my practice, I ask patients to avoid  nicotine in all its "modalities' of delivery 6 weeks prior to surgery. It is a powerful constrictor of blood vessels, decreasing blood flow to the “flaps” used during these procedures. This decreased blood flow could potentially lead to wound healing problems and/or tissue necrosis. 
Best advice: avoid nicotine completely as long as possible prior to surgery and then do not restart.
Best wishes.