Q. Does smoking have any affect on your milk supply when breastfeeding?
A. It can. However, it depends on how much you smoke. The American Academy of Pediatrics would rather have you breastfeed, if you are smoking, to give the baby the health benefits of the antibodies, than have a mother who smokes and giving the baby formula.
The half life of a cigarette is 97 minutes or roughly an hour and a half. So if you are smoking, smoke after the baby has eaten. Also it is a good idea to wear a "smoking coat"--some article of clothing that you cover up with when you smoke, because the clothing you are wearing has the aftereffects of secondhand smoke. Also don't smoke in the house. Smoking leads to increased incidence of upper respiratory infections in small children. Smoking also can cause preterm labor.
If you can't quit, at least cut down. There are many stop smoking clinics now, that have great success in helping a person stop.
PS . . . I am an ex-smoker who smoked while being pregnant and nursing my first child. I quit when I got pregnant with my second child. It was terribly difficult, but because I was pregnant I decided I needed to do it for my daughter. That was 20 years ago, now.