Several studies involving human participants have found that ginseng may lower blood sugar levels in people with type 2 diabetes.
For example, in a study published in 2000, researchers gave capsules of North American ginseng (Panax quinquefolius) to people with diabetes who were also receiving conventional treatment in the form of diet or prescription drugs.
In their analysis, the researchers found that subjects receiving a 3 gram dose of ginseng had a blood sugar level that was 59.1% less than subjects who had received the placebo.
More research is needed, however, because the long-term effects of ginseng aren't known. Also, it's not known how ginseng interacts with prescription diabetes medication.
People with diabetes should not take ginseng instead of standard treatment and should not combine ginseng with their prescription drugs unless supervised by a health care professional.
Vuksan V, Stavro MP, Sievenpiper JL, Beljan-Zdravkovic U, Leiter LA, Josse RG, Xu Z. Similar postprandial glycemic reductions with escalation of dose and administration time of American Ginseng in Type 2 Diabetes. Diabetes Care 23(9):1221-1225, 2000.