The only way to be certain of avoiding the risks of smoking is not to smoke. And reducing the health risks of smoking has been the overriding aim of tobacco research for many years.
It is known that the risk of developing smoking-related disease is greater in people who smoke more cigarettes per day and for longer periods.
Several decades have been spent researching the nature of tobacco smoke, identifying key toxicants and developing technologies to reduce the levels of some toxicants in smoke.
Laboratory tests show that the technologies successfully reduce levels of some, though not all, toxicants in smoke.
This is the first clinical study of test products and it shows an average reduction in smokers' exposure to certain toxicants over the study period.
"There are already tobacco and nicotine products available, such as snus and e-cigarettes, that are known to pose substantially lower risk than cigarettes. And we don't know whether it will be possible to scientifically prove that reduced toxicant cigarettes reduce health risks," Dr David O'Reilly, Group Scientific Director at British American Tobacco said.
"But, we believe reducing smokers' exposure to cigarette smoke toxicants continues to be an important research objective, given the numbers of people who smoke and the numbers who are likely to continue to smoke for the foreseeable future," he said.
The prototype cigarettes incorporate several toxicant-reducing technologies - two related to the tobacco and two in the filter.
A tobacco-processing technique employs an enzyme to remove proteins and polyphenols that become toxicants when burned. An inert tobacco substitute containing calcium carbonate and glycerol was also added, which dilutes the smoke.
The filter technologies include a resin that filters out aldehydes produced as a result of burning sugars in the tobacco and a novel activated carbon with an internal nanostructure optimised for trapping certain volatile smoke toxicants.
The results are published in the journal Regulatory Toxicology and Pharmacology.