Quit218-12 hours after your last cigaretteOxygen gets its seat back
By Yevhenii, who smoked for 26 years · Updated 30 Oct 2026 · 2 min readWhat's happening in your body
Smoke carries carbon monoxide, and haemoglobin holds on to it about two hundred times more tightly than it holds oxygen. Each molecule of it takes a seat that oxygen was supposed to have. Breathing ordinary air, the body clears half of it every four to five hours. No more is arriving, so by now the level has at least halved and the freed seats are carrying oxygen again.
What to expect
Nicotine has a half-life of about two hours, so most of your last dose is already gone. Withdrawal usually starts within a few hours of the last cigarette, and the first full craving tends to show up around now. It builds, peaks and fades within a few minutes, and it does that whether or not you smoke. The single most useful thing to know about a craving is that it ends by itself.
Alongside it you may notice restlessness, a shorter temper, or a vague sense that something is missing. All of it is the start of the normal course, not a sign that anything is going wrong.
Try this
Time the next craving on your phone, from the first pull to the moment it loosens. Every later craving can then be held against a number you measured yourself, so you know roughly when it will ease.
What else you could do
While you wait for it to pass, move. A few minutes of brisk walking or a flight of stairs takes the edge off. Breathe in slowly through the nose and out through the mouth, a few times over. Keep your mouth busy with something to chew, a carrot, celery, sugar-free gum. And if it is late, go to bed early. A first evening that ends at ten is shorter than one that ends at one.
Sources. NHS Better Health, Quit smoking. Benowitz NL, Hukkanen J, Jacob P. Nicotine chemistry, metabolism, kinetics and biomarkers. Handb Exp Pharmacol, 2009. NHS Better Health, Managing nicotine withdrawal symptoms.