I think grade B scientific evidence to use ginseng for mental performance and type 2 diabetes is good.
We followed B recommendations all the time in the clinic. For example, recommendation to screening for colorectal cancer with FOBT, sigmoidoscopy, or both received a B recommendation from USPSTF.
In the reference section, Vuksan V, Sievenpiper, and Koo Vy publised an article in the Arch of Internal Medicine in 2000 regarding the hypoglycemic effect of ginseng.
I use it all the time and it keeps me alert and excuses to eat more candies (to get my blood sugar up)
A recommendation = USPSTF strongly recommends that clinicians provide the service to eligible patients, based on good evidence that the service improves important health outcomes and that benefits substantially outweigh harms.
B recommendation = USPSTF recommends that clinicians provide the service to eligible patients, based on at least fair evidence that the service improves important health outcomes and that benefits outweigh harms.
C recommendation = USPSTF makes no recommendation for or against providing the service, based on at least fair evidence that the service can improve health outcomes but the balance of benefits and harms is too close to justify a general recommendation.
D recommendation = USPSTF recommends against routinely providing the service to asymptomatic patients, based on at least fair evidence that the service is ineffective or that harms outweigh benefits.
I recommendation = USPSTF concludes that the evidence is insufficient to recommend for or against routinely providing the service, based on evidence that is lacking, of poor quality, insufficient, or unable to determine the balance of benefits and harms.