The health dangers of smoking tobacco have been known for centuries. In 1604 King James I of England described tobacco as harmful to the brain and lungs, among other ill effects, and urged his subjects to avoid it. During the next 300 years, opinions varied as to whether tobacco is beneficial or harmful to the body. Some argued against tobacco as an immoral substance.

In 1926 a Cambridge University professor, Sir Humphrey Rolleston, gave a lecture to a medical society in which he listed some possible toxic effects of nicotine. These included irritation of the throat and upper air passages and heart disorders such as irregular heartbeat and angina, pain caused by insufficient blood reaching the heart. However, he did not believe that tobacco was a drug of addiction.

But even as Rolleston was lecturing, researchers were looking at evidence suggesting that smoking was responsible for the...