The first three days are the hardest
Nicotine has a half-life of about two hours. By 8 hours after your last cigarette, blood carbon-monoxide levels have already halved. By 72 hours, blood nicotine is functionally zero — which is also when withdrawal symptoms peak: irritability, low mood, difficulty concentrating, increased appetite. Pharmacotherapy (NRT, bupropion, varenicline) compresses this window dramatically. The 2008 US Public Health Service guideline puts combination NRT (24-hour patch + short acting gum or lozenge) and varenicline at roughly double the long-term quit rate of cold-turkey attempts.
One year is the cliff
The single largest health gain happens at one year: coronary heart disease risk drops to roughly half that of a continuing smoker. At 5 years, stroke risk approaches that of a never-smoker, and risk for cancers of the mouth, throat, esophagus and bladder is roughly halved. At 10 years, lung-cancer death rate is about half that of a continuing smoker. At 15 years, coronary heart disease risk is indistinguishable from a never-smoker. None of these milestones reverse if you start again — every one of them resets to zero.
Make the numbers visible
One of the most reliable cessation strategies in the behavioural literature is “earmarking” — physically segregating the money you would have spent on cigarettes into a separate account or jar. The Cochrane review on financial incentives for smoking cessation (2021) finds modest but durable effects. At a pack-a-day Canadian smoker buying mid-tier brands at ~$17/pack, that is roughly $6,200 per year. Five years of saving funds a vacation; ten funds a downpayment.