The idea is to stop at least 3 days prior to surgery and for at least 3 days after your hair transplant procedure. Try not to smoke any products, tobacco and weed included, at least 24 hours prior to your hair transplant procedure as smoking will slow down healing and increase the chances of wound infection and scarring.
Smoking (nicotine) inhibits blood flow to the skin and scalp by constriction of blood vessels, the blood carries more oxygen than in normal circulation.
All this can result in bad healing, increased scarring, and can also make the whole procedure very bloody and messy for the surgeons.
Some even suggest stopping 2 weeks prior and continue smoking only 1-month post-op. Each doctor to is own if you're coming to Dr. Cole for surgery, the surgical team will give you full pre-op instructions.
By the way, no alcohol and coffee 3 days prior to your hair transplant procedure as well. Coffee also increases blood flow.