Alternative Medicine Review 2009 (Jun); 14 (2): 172–176 ~ FULL TEXT
Panax ginseng, used medicinally for thousands of years in China, Korea, and Japan,  is well known as an adaptogen and a restorative tonic that is widely used in traditional Chinese medicine (TCM) and Western herbal preparations. [2, 3] Eclectic uses for Panax ginseng include fatigue, infertility, liver disease, amnesia, colds, menopause, and erectile dysfunction. [2-4] There are many species of Panax, which leads to some confusion in the literature. However, the two species that have been the most extensively researched and used are Panax ginseng and Panax quinquefolius. Another botanical species, although commonly called Siberian ginseng (Eleutherococcus senticosus), is not a true ginseng. This monograph reviews the constituents, mechanism of action, safety, and clinical efficacy of Panax ginseng.
A double-blind, placebo-controlled eight-week study examined the immune effects of 100 mg Ginsana[R] (G115), 100 mg liquid ginseng extract, or placebo twice daily in 60 healthy volunteers. Blood samples collected at baseline, week four, and week eight examined polymorphonuclear (PMN) cell chemotaxis, phagocytosis, total lymphocytes, T-helper and T-suppressor cells, and NK-cell activity. The groups receiving ginseng experienced consistent improvement in immune system activity at week four and statistically significant differences at week eight, evidenced by improvements in PMN cell chemotaxis, phagocytosis, and total number of T-helper and T-suppressor cells. The authors concluded ginseng extract stimulates the immune system and the standardized extract is more effective than the liquid ginseng extract. 
Some of the same researchers examined the effects of Panax ginseng extract on the immune response to vaccination. The multicenter, 12-week, double-blind RCT compared immune response in 227 participants, measured as NK-cell activity, at weeks eight and 12, post influenza vaccine given at week four. The treatment group received 100 mg G115 twice daily. NK-cell activity for the ginseng group was double that of the placebo group (p<0.0001) at weeks eight and 12. Serum antibody titers were 272 units in the ginseng group compared to 171 units in the placebo group. A significant decrease in the frequency of upper respiratory infections during weeks 4-12 was noted in the treatment group compared to placebo; 15 cases versus 42 cases, respectively. This study supports the role of ginseng in immune system modulation. 
An RCT compared the effects of red Panax ginseng on HIV-1 infected patients (n=61).  The purpose of this study was to determine the effects of red Panax ginseng after accounting for HLA type (I or II and class A, B, and C), on CD4 counts, CD8 counts, and the trend toward decreased resistance to antiretroviral drugs. HLA type can be associated with an improved prognosis in HIV patients, based on an algorithm that also predicts risk of disease progression. 
The treatment group received 5.4 g red Panax ginseng daily. Blood samples were taken from the control group (n=199) and HIV-1 infected patients every six months throughout the study. Data analysis revealed an inverse correlation between the HLA score and the decrease of CD4 T cells over time, a decrease in the decline of CD4 T cells associated with the intake of red Panax ginseng, and a significant (p<0.05) decline of CD4 T cells, independent of the HLA class I effects on immune system cells. The authors concluded that red Panax ginseng and HLA type independently affect the slow depletion of CD4 T cells in HIV-infected patients.
Eclectic medicine texts reference Panax ginseng for its beneficial use in blood sugar regulation. [2, 10] In a double-blind RCT, Sotaniemi et al examined the efficacy of Panax ginseng in newly diagnosed type 2 diabetics.  Parameters measured included physical performance, mood, serum lipids, fasting blood glucose, hemoglobin A1c (HbA1c), aminoterminal propeptide (PIIINP) concentration, and body weight. PIIINP serum levels are associated with coronary artery disease and were used as a safety parameter in this study. The study participants (n=36) were given 100 mg ginseng extract, 200 mg ginseng extract, or placebo daily for eight weeks. Compared to the placebo group, the 200-mg ginseng group experienced elevated mood, improved physical performance, and reduced fasting blood glucose. The authors concluded
A 2005 double-blind, crossover RCT examined the effects of Panax ginseng on blood glucose levels and cognitive performance during sustained mental activity.  Healthy young adults (n=30) took a 10-minute test battery for baseline results, then were given 200 mg G115, 400 mg G115, or placebo. One hour later the test battery was repeated six times in rapid succession. Blood sugar levels were assessed at baseline and twice during the testing procedure. The 200-mg and 400-mg G115 doses reduced blood glucose levels significantly (p<0.005). Significant improvement was also noted in the ability to complete the serial sevens subtraction task after taking 200 mg G115 (p<0.05). The authors concluded Panax ginseng improves mental performance, possibly by regulating glucose metabolism.
A double-blind, 12-week RCT examined the effect of red Panax ginseng on HbA1c levels in 19 subjects with well-controlled type 2 diabetes.  Study participants received 2 g ginseng or placebo three times daily before meals. Plasma glucose and insulin, insulin sensitivity, and oral glucose tolerance were secondary measures of efficacy, while blood pressure checks and liver and kidney function tests assessed safety. Although no change was seen in HbA1c levels with ginseng, the participants remained well controlled throughout the study without pharmaceutical intervention--with average levels of HbA1c of 6.5 percent. A significant 8- to 11-percent decrease in glucose on the oral glucose tolerance test and 33-percent decrease in plasma insulin (p<0.05) was seen in the ginseng group compared to placebo. No change was reported in safety parameters throughout the study, which led the authors to conclude red Panax ginseng is safe to use in the treatment of type 2 diabetes.
Warnings and Contraindications
The German Commission E and the World Health Organization report no known contraindications for Panax ginseng. [3, 12] Caution is advised during pregnancy and lactation due to a lack of controlled human clinical studies. [3, 5] Teratogenicity has been documented in an in vitro rat embryo model, but the implication for human health is questionable due to dosages used that exceed possible human consumption.  In Asian countries the use of Panax ginseng in TCM formulas is common throughout pregnancy and lactation.