Twenty minutes after quitting smoking, the blood pressure and heart rate drop, and after 12 hours, the carbon monoxide level in the blood drops back down to normal, according to the American Cancer Society. After two weeks to three months, circulation improves and lung function increases.
After one to nine months, the lungs of people who have quit smoking can handle mucus and clean themselves properly, have less risk of infection, and have less difficulty with breathing, states the American Cancer Society. After a year, the risk of coronary heart disease is cut in half compared to a continued smoker, and after five years, the risks of cancer in the mouth, throat, esophagus and bladder are also cut in half. The risk of cervical cancer is reduced to that of a non-smoker.
The risk of stroke decreases to that of a non-smoker after two to five years, reports the American Cancer Society. The risks of laryngeal and pancreatic cancer decrease after 10 years, as does the risk of dying from lung cancer. Fifteen years after a person has stopped smoking, the risk of coronary heart disease drops to that of a non-smoker. People who quit smoking also lower their risk of diabetes.