Researchers at the Harvard School of Public Health said consumers were not made aware that their brand had been altered -- changes that may have exceeded acceptable product variance guidelines.
"I hope the Food and Drug Administration requires disclosure of any changes made to tobacco products and that the changes are disallowed if shown to increase appeal, addiction and harm," Greg Connolly, director of the Tobacco Control Research Program at Harvard School of Public Health, said in a statement.
Connolly and lead author Geoffrey Ferris Wayne studied internal tobacco company documents released following the 1998 Master Settlement Agreement. The documents describe significant changes made to commercial products over time, including blend, processing, casing, flavoring and physical design features.
For example, new methods were developed to process tobacco, altering the smoke chemistry and the form of nicotine delivery, the study said.
"Even incremental changes that occur over a period of years can result in significant design differences," Wayne said.
"The resulting product may have altered chemistry or delivery, yet the smoker is largely unaware of these changes. This underscores the need for industry transparency and accountability."
The study is published online ahead of print in the Journal of Tobacco Control.