British and American tobacco companies deliberately added powerful appetite-suppressing chemicals to cigarettes to attract people worried about their weight, according to internal industry documents dating from 1949 to 1999.
Chemical additives are just one of several strategies successfully used by tobacco companies over the past 50 years to convince people that smoking makes you thin.
Tobacco giants Philip Morris and British American Tobacco added appetite suppressants to cigarettes, according to the documents, released during litigation in the US. Four other major companies tested potential chemicals, including amphetamine and nitrous oxide, better known as laughing gas, but the documents, which are incomplete, do not reveal if such chemicals were ever added and sold to the public.
The presence of appetite-suppressing chemicals could help explain why smokers who quit often gain weight, according to Swiss researchers in the European Journal of Public Health. They call for stricter rules on tobacco additives amid suggestions that sensitive documents are being removed from databases by the industry to avoid disclosure.
Critics say this is further evidence of tobacco companies targeting smokers concerned with weight gain. They argue that the industry continues to exploit such anxieties through sophisticated marketing and packaging, which they are pressing the government to ban.
Professor David Hammond, a tobacco industry expert at Waterloo University, Ontario, Canada, said: "We know the industry explored ways to exploit concerns about weight loss back in the Sixties, because they knew it was an issue that concerned women, who they wanted to recruit as smokers. We don't know if appetite-suppressing molecules are still added, because compliance with additive regulations is poor and sensitive internal documents are usually shredded."
By the end of the 20th century, smoking was almost exclusively male behaviour, but the number of women smokers dramatically increased in the 1940s and 1950s. Today, one in five British men and women smoke, causing more than 100,000 preventable deaths a year.
A Canadian study of 500 young women, published in Tobacco Control this month, found those looking at female-oriented cigarette packs branded with words such as "slim" and "vogue", were more likely to believe smoking helps people control their appetite – an important predictor of smoking among this group – compared with those viewing plain packaging. Smokers wrongly believe that certain words, such as the names of colours, and long, slim cigarettes mean the brand is less harmful, according to a study, that included 2,000 Britons, published in Addiction.
Since the widespread advertising ban, images such as Kate Moss smoking on the catwalk have become invaluable for the industry.
Last year, Australia became the first country to introduce compulsory plain packaging. Here, the Government committed to considering similar controls on packaging in the Tobacco Control Plan published in March. The public health minister Anne Milton will meet her Australian counterpart in the next few weeks.
Action on Smoking and Health (Ash) is urging the Health Select Committee to force tobacco companies to disclose documents that would shed light on marketing strategies, including product packaging and design, to help MPs make an informed choice about introducing plain packaging.
Deborah Arnott, chief executive of Ash, said: "Now advertising is banned, the industry uses pack design and product descriptors, such as "slims", to promote the message that smoking makes you thin. It must be required to put its products in plain, standardised packaging to prevent it using such "dog whistle" tactics to promote smoking to vulnerable young women."
A Tobacco Manufacturers' Association spokesman said: "We do not believe any plans for plain packaging are based on sound public policy, nor any compelling evidence... Plain packs are likely to lead to further increases in smuggling... and make it easier for counterfeiters to copy."