The herbal ingredient -- extract of Garcinia -- reduced bad breath levels by about 60 percent from the baseline, compared with a placebo's 26 percent, says Hamad Aljufairi of the Medical University of Bahrain, a branch of the Royal College of Surgeons in Ireland.

The Garcinia study was one of five studies included in a systematic review involving 293 bad breath sufferers.

"Because most mouthwash treatments seem to work, careful and strict experimental design and implementation are required," study co-author Aljufairi, said in a statement.

The studies took place in Thailand, Israel, Holland, Spain and the United States. Two of the studies measured Listerine against placebo, and one of the two measured ingredients found in some mouthwashes: cetylpyridinium chloride and zinc chloride.

The reviewers concluded that chlorhexidine-containing mouthwashes, found in some brands on drug store shelves, "have been shown to be successful in reducing antibacterial activity -- on the tongue and thus are seen as potentially effective agents in controlling halitosis." However, chlorhexidine, "also has some disadvantages, principally with the increased tooth and tongue staining, bad taste and reduction in taste sensation."