Herbs that may be helpful
Echinacea has long been used for colds and flu. Double-blind trials in Germany have shown that infections associated with flu-like symptoms clear more rapidly when people take echinacea.4 Echinacea appears to work by stimulating the immune system. The usual recommended amount of echinacea is 3-5 ml of the expressed juice of the herb or tincture of the herb or root, or 300 mg of dried root powder three times per day.
The effect of a syrup made from the berries of the black elderberry on influenza has been studied in a small double-blind trial.5 People receiving an elderberry extract (four tablespoons per day for adults, two tablespoons per day for children) appeared to recover faster than did those receiving a placebo.
In a preliminary study of elderly nursing home residents in Japan, only 1.3% of those who gargled with a green tea extract three times a day during the winter developed influenza, whereas 10.4% of those who gargled without the green tea extract developed the disease (a statistically significant difference). The presumed active ingredients in the extract were a group of flavonoids called catechins, which were present in the extract at half the concentration as that in green tea.6 It is possible, therefore, that gargling with green tea itself might also be effective for preventing the flu.
Asian ginseng and eleuthero (Siberian ginseng) have immune-enhancing properties, which may play a role in preventing infection with the influenza virus. However, they have not yet been specifically studied for this purpose. One double-blind trial found that co-administration of 100 mg of Asian ginseng extract with a flu vaccine led to a lower frequency of colds and flu compared to people who just received the flu vaccine alone.7
Boneset has been shown in test tube and other studies to stimulate immune-cell function,8 which may explain it's traditional use to help fight off minor viral infections, such as the flu.
Wild indigo contains polysaccharides and proteins that have been reported in test tube studies to stimulate the immune system. The immune-enhancing effect of wild indigo is consistent with its use in traditional herbal medicine to fight the flu.9 However, wild indigo is generally used in combination with other herbs such as echinacea, goldenseal, or thuja.
While not as potent as willow, which has a higher salicin content, the salicylates in meadowsweet do give it a mild anti-inflammatory effect and the potential to reduce fevers during a cold or flu. However, this role is based on historical use and knowledge of the chemistry of meadowsweet's constituents; to date, no human studies have been completed with meadowsweet.