Astragalus for the Immune System

I've just been told that astralagus is good for immune problems. Is this true? Any side effects? What dosage & what time of the day to take it? Derivatives?

Astragalus, the Chinese herb Huang Qi, has strong anti-viral and anti-bacterial activities. It's activity in enhancing the immune system is to increase the white blood cell count to improve defense against disease-causing micro-organisms, and to increase interferon production to act against viruses. It has been used in China for these activities for 2000 years. Western herbalists often use Astragalus instead of, or as well as Echinacea where the immune system needs boosting.
Some uses of Astragalus are: Chronic Fatigue (Myalgic Encephomyelitis), influenza, the common cold, pneumonia, myocarditis and infection of the urinary tract. Thomas Bartram, in "Encyclopedia of Herbal Medicine" (Grace Publishers, Mulberry Court, Stour Road, Christchurch, Dorset, BH23 1PS, England) states that it inhibits HIV-1 replication in cells acutely or chronically infected.
Dosage would be according to the bottled preparation, or 2 teaspoons of dried root simmered gently in a cup of water for 15 minutes, one half to one cup three times a day. It would be most effective taken between meals. There are no known side effects.