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.¹⁸

Double-blind trials have shown that common cold symptoms improve^19,20 and recovery is faster²¹ when andrographis extract containing 48 to 60 mg andrographolides is taken in three or four divided doses daily, beginning as soon as possible after symptoms appear. In addition, preliminary research in Russia suggests andrographis extract may be effective for the treatment of influenza.²² This extract was also tested for preventing colds in a double-blind study of teenagers.²³ After three months, the group taking 5 mg of andrographolides twice daily had only half the number of colds experienced by the placebo group.

Other preliminary²⁴ and double-blind^25,26 research has shown similar benefits for treating the common cold from a combination of andrographis extract and an eleuthero extract containing 2.0 to 2.4 mg per day eleutherosides.

Immune-modulating plants that could theoretically be beneficial for people with HIV infection include Asian ginseng, eleuthero, and the medicinal mushrooms shiitake and reishi. One preliminary study found that steamed then dried Asian ginseng (also known as red ginseng) had beneficial effects in people infected with HIV, and increased the effectiveness of the anti-HIV drug, AZT.²⁷ This supports the idea that immuno-modulating herbs could benefit people with HIV infection, though more research is needed.

The herbs discussed here are considered members of a controversial category known as adaptogens, which are thought to increase the body's resistance to stress, and to generally enhance physical and mental functioning.^28,29 Many animal studies have shown that various herbal adaptogens have protective effects against physically stressful experiences,^30,31 but whether these findings are relevant to human stress experiences is debatable.

Animal research has reported antistress effects of Eleutherococcus senticosus (also known as Siberian ginseng),³² and Russian research not available in the English language reportedly describes human studies showing similar effects in humans.^28,34 A double-blind study of healthy elderly people reported that those who took 60 drops per day of a eleuthero liquid extract (concentration not specified) scored higher in some quality-of-life measures after four weeks, but not after eight weeks, compared with a group taking a placebo.³⁵ Athletes experiencing the stress of training who took an eleuthero extract equivalent to 4 grams per day had no changes in their blood levels of an adrenal stress hormone after six weeks.³⁶ More research is needed to clarify the value of eleuthero for treating stress.

Eleuthero(Eleutherococcus senticosus) supplementation may improve athletic performance, according to preliminary Russian research.³⁶ Other studies have been inconclusive and two recent double-blind studies showed no beneficial effect on endurance performance in trained men.^37,38,39 Eleuthero strengthens the immune system and thus might reduce the risk of post-exercise infection. Although some doctors suggest taking 1 to 4 ml (0.2 to 0.8 tsp) of fluid extract of eleuthero three times per day, evidence supporting the use of this herb to enhance athletic performance remains weak.

Adaptogenic herbs such as Asian ginseng and eleuthero may also be useful for CFS patients—the herbs not only have an immunomodulating effect but also help support the normal function of the hypothalamic-pituitary-adrenal axis, the hormonal stress system of the body.⁴¹ These herbs are useful follow-ups to the six to eight weeks of taking licorice root and may be used for long-term support of adrenal function in people with CFS. However, no controlled research has investigated the effect of adaptogenic herbs on CFS.

One study found that an eleuthero extract improved symptoms in patients suffering from mild-to-moderate chronic fatigue. However, after one month of treatment, the benefit began to wane, and eleuthero was not more effective than a placebo after two months of treatment.These findings support the observation of herbalists that eleuthero is more effective when used in a pulsed manner (a few weeks at a time) than when used continuously.