New York, Aug 18 (IANS): Even a drug that helps people kick the butt may not increase the number of those who do so, says a new study which suggests that inspiring smokers to quit is as important as aids that enable them do so.

The study found that introduction of a new prescription smoking-cessation drug varenicline in 2006 has had no significant impact on the rate at which US adults successfully quit smoking.

The findings suggest that the primary effect of varenicline (marketed as Chantix) has been to displace the use of older tobacco addiction therapies, such as nicotine patches and the antidepressant, bupropion (Zyban).

"We had hoped the new pharmacotherapy would help more people quit, but this is not what is happening," said lead author Shu-Hong Zhu, professor at University of California, San Diego School of Medicine in the US.

"Instead, varenicline is replacing other options like the patch, without having any significant population-level impact on quitting success," Zhu noted.

According to the US Centers for Disease Control, almost 20 percent of U.S. adults 18 years or older are cigarette smokers.

For the study, the researchers analysed two US Census Bureau surveys of smokers age 18 and older, conducted in 2003 and 2010-11, before and after varenicline became commercially available.

Based on responses from more than 39,000 smokers, overall use of pharmacotherapy increased from 28.7 percent of smokers trying to quit in 2003 to 31.1 percent in 2010-11, representing a 2.4 percent increase.

This slight increase in the use of cessation aides, however, did not translate into more smokers breaking the habit.

In 2003, approximately 4.5 percent of smokers reported successfully quitting for at least a year, compared with 4.7 percent in 2010-11.

"We are not saying Chantix does not help smokers quit. It does, but it won't solve America's tobacco epidemic unless it inspires more smokers to try to quit," Zhu explaiined.

Globally, tobacco use is estimated to cause nearly six million deaths annually.

The study was published online in the journal Tobacco Control.