Now that nicotine replacement therapy such as nicotine patches and gums are sold without a prescription, they may be less effective at helping smokers kick the habit for good, new study findings show.

One problem is that most people who buy these products don't use them for six weeks -- the minimal time recommended, according to the report. However, it is also possible that nicotine replacement therapies are not as effective as once thought.

"This study adds to concerns that the efficacy of pharmaceutical aids observed in clinical trials may not extend to effectiveness in the general population," according to Dr. John P. Pierce and Elizabeth A. Gilpin of the University of California, San Diego.

The findings appear in the latest issue of The Journal of the American Medical Association.

Pierce and Gilpin obtained their results from a review of three recent tobacco surveys conducted in California between 1992 and 1999, each of which asked between 5,000 and 10,000 people about their tobacco use.

The investigators found that the proportion of smokers who tried to quit increased by 61 per cent, from 38 per cent in 1992 to 62 per cent in 1999. The proportion of people opting for nicotine replacement therapies to help them quit also increased by 50 per cent during the same period, from 9 per cent to 14 per cent. In 1999, a total of 17 per cent of quitters were using nicotine replacement therapy, an antidepressant, or both to help them butt out for good.

The authors note that nicotine replacement therapy appears to help moderate to heavy smokers (at least 15 cigarettes per day) quit in the short-term. However, the nicotine replacement therapies appeared to offer no boost in users' chances of kicking the habit for good once the products became available over-the-counter in 1996.

In addition, Pierce and Gilpin write that they could find no benefit of nicotine replacement therapies in helping light smokers quit, either in the short- or long-term. Almost 60 per cent of the people included in the tobacco surveys were classified as light smokers.

Despite the apparent lack of benefit of the products, sales increased more than threefold from 1992 to 1999, the report indicates.

Pierce and Gilpin suggest that trials of nicotine replacement therapy may have included people who were more motivated to quit than smokers in the general population, or may have been too generous when determining whether or not a former smoker had quit for good. In one study, smokers were considered to have quit if they were abstinent for at least one week at 5 months.

According to GlaxoSmithKline, a maker of nicotine replacement products, previous studies have demonstrated that over-the-counter nicotine replacement therapies can increase a smoker's chances of quitting just as well as when the products require a prescription. Furthermore, previous research has shown that using nicotine replacement products can double a smoker's chance of quitting, relative to those who try to butt out without relying on the products.

"Quitting smoking can be a tough challenge for many smokers, but the results from California should not discourage smokers from striving to escape their tobacco dependence and using clinically proven cessation aids and behavioral support to increase their chances of success," the company said in the statement.