The evidence is mixed on herbal products that claim to boost immunity this flu season, medical experts say.

Dozens of products are sold in stores and online, claiming to prevent flu by boosting the immune system. Some of the claims have sparked investigations by Canada's Competition Bureau.

Tips from Competition Bureau

If consumers suspect that a website contains deceptive marketing or fraudulent claims related to the H1N1 virus, they may contact the Competition Bureau.

The bureau's tips include:

  • Beware of ads that promise too much.
  • Think twice before buying a product that claims it can do it all.
  • Steer clear of a product that claims to be a "scientific breakthrough."
  • Genuine scientific discoveries make front-page news. If the first or only place you learn about a new treatment is through an advertisement on the internet, be suspicious.
  • Keep your guard up when ads mention "scientific evidence."
  • Ads that are long on technical jargon may be short on proof. The presence of a doctor in an ad is no guarantee the product works. Scam artists have been known to dress models to look like experts.
  • Don't be swayed by a questionable "success story" or so-called "patient testimonial."
  • Despite what the company claims, there's no guarantee that "John Doe of Hometown, Canada" has achieved the advertised results, or is even a real person.
  • A money-back guarantee is no proof that a product works.
  • A promise of a "money-back guarantee" does not necessarily mean you will get your money back from the scam.
  • Scam artists who offer a guarantee have been known to "take the money and run."
  • Consult your health-care practitioner before trying any new treatment.
  • A doctor, nurse or health-care professional who knows your medical condition is your best source of information.

Herbs such as ginseng and echinacea make the body produce more immune cells and enhance the way some cells work. But no one has been able to show conclusively whether that translates into stronger overall immunity to ward off infections.

"I think when someone says 'immune booster' you have this idea that you are going to get this dramatic effect," said Heather Boon, a pharmacy professor at the University of Toronto.

"With most of these herbs, that's just not what happens. If there is any effect at all, they may decrease the duration or severity of your symptoms. So instead of being sick for 10 days, you may be sick for nine or 9½ days. It's not a dramatic difference."

Health Canada has reviewed and approved one new product on the market. ColdBuster is a supplement to maintain immune functions during flu season. The orange-flavoured liquid contains vitamins C, B6 and B12, along with zinc.

"The claims we're allowed to make is, 'The ingredients in ColdBuster help fight colds and flus,'" said Roman Katsman, sales manager for Toronto-based ColdBuster Remedies.

Some studies have found benefits from supplements such as vitamin C, zinc, echinacea or ginseng. Others have found no benefit.

There is a lack of concrete evidence because the immune system is so complex and there is no way to measure the activity of the immune system as a whole, said Dr. Carl Weiss, an immunologist at Hôpital Maisonneuve-Rosemont in Montreal.

"In spite of being studied for a long time and people claiming that using certain medications, vitamins, whatever will increase your immune system, there hasn't been anything proven so far."

Herbals can't replace the H1N1 vaccine, the only clinically proven way to prevent swine flu, Boon said.

Most experts said supplements won't hurt, but people shouldn't bank on them. And overall, Canadians getting proper nutrition probably don't need an immune boost.