Researchers have found that the herb Echinacea, a herb used for colds, don’t help relieve any symptoms.
Based on their findings, the researchers say they cannot recommend the popular herbal remedy to cold sufferers. But they are not advising people against using it, either.
Echinacea, which is derived from the coneflower, has long been touted as a way to bolster immunity and prevent or ease the common cold.
Over the years, though, studies have come to conflicting conclusions as to whether the herb really works. And even the positive ones have generally suggested modest benefits at best.
Echinacea a placebo
In this latest study, published in the Annals of Internal Medicine, researchers pitted an echinacea supplement against placebo for easing cold symptoms among 719 adults and teenagers.
They found that echinacea users recovered slightly more quickly, an average of a half-day sooner, and reported somewhat less severe symptoms.
Small differences not significant
"This echinacea formulation, which is a good one, did not show any major effect," said lead researcher Dr Bruce Barrett, of the University of Wisconsin-Madison.
On the other hand, he said, the findings do not rule out the possibility of a modest benefit.
Dr Barrett said that while some experts will consider this study the "final nail in the coffin" for echinacea as a cold fighter, the positive findings from some past studies complicate the picture.
"Before this trial, the evidence was inconclusive," Dr. Barrett said. "And I don't think we're past the inconclusive stage."
What it means for cold sufferers
"If you're an adult who has tried echinacea in the past and been happy with it, this study does not say you should stop using it," he said. "On the other hand, it certainly doesn't tell you, that you should start."
The problem with the common cold is that it can be caused by any of over 200 different viruses. There are treatments that can make symptoms less severe, but nothing - from cold medications to vitamin C seems to speed recovery.
For the current study, Dr Barrett's team recruited 719 12- to 80-year-olds who had developed cold symptoms within the past 36 hours. They randomly assigned the patients to take nothing, use placebo tablets or use echinacea tablets.
Half the echinacea users knew they were taking the herb, but the other half were unaware of whether they were taking echinacea or placebo.
The echinacea groups took a formulation made from the root of the plant, which is rich in constituents that, some studies suggest, would be most likely to battle cold symptoms. The patients took eight echinacea tablets on the first day of the study, then four a day over the next four days.
On average, people in both echinacea groups suffered cold symptoms for between six and seven days. The placebo and no-pill groups differed from them by only a matter of hours, roughly a half-day.
Similarly, there was no clear difference when the researchers looked at the groups' self-rated symptom severity, which each patient had recorded twice a day while the cold lasted.
No side effects
The researchers found no evidence that echinacea users suffered side effects, like headache, stomach upset or diarrhoea, at a higher rate than the untreated groups.
That's in line with the low risk of side effects studies have generally found when echinacea is taken as directed -though there is a small chance of allergic reaction.
As far as effectiveness, however, even the studies with positive results suggest echinacea has only modest benefits against cold symptoms.
"No large, well-done clinical trial has shown a large benefit," Dr Barrett said. "It doesn't stop a cold in its tracks, that's for sure."
The current study was funded by the US National Institutes of Health and the Robert Wood Johnson Foundation.
(Reuters Health, Amy Norton, December 2010)